diff --git a/app/api/routers/essentials.py b/app/api/routers/essentials.py
index 7279ce0..2aab585 100644
--- a/app/api/routers/essentials.py
+++ b/app/api/routers/essentials.py
@@ -1,7 +1,7 @@
 """Essentials API router — CRUD for Essentials nested under a Proposal.
 
 Endpoints are scoped to a project and proposal:
-    /projects/{project_id}/proposals/{proposal_id}/essentials
+    /projects/{project_code}/proposals/{proposal_code}/essentials
 
 Only open Proposals allow Essential mutations.
 """
@@ -26,7 +26,7 @@ from app.services.activity import log_activity
 from app.services.essential_code import generate_essential_code
 
 router = APIRouter(
-    prefix="/projects/{project_id}/proposals/{proposal_id}/essentials",
+    prefix="/projects/{project_code}/proposals/{proposal_code}/essentials",
     tags=["Essentials"],
 )
 
@@ -35,53 +35,27 @@ router = APIRouter(
 # Helpers
 # ---------------------------------------------------------------------------
 
-def _find_project(db: Session, identifier: str):
-    """Look up project by numeric id or project_code."""
-    try:
-        pid = int(identifier)
-        p = db.query(models.Project).filter(models.Project.id == pid).first()
-        if p:
-            return p
-    except (ValueError, TypeError):
-        pass
+def _find_project(db: Session, project_code: str):
+    """Look up project by project_code."""
     return db.query(models.Project).filter(
-        models.Project.project_code == str(identifier)
+        models.Project.project_code == str(project_code)
     ).first()
 
 
-def _find_proposal(db: Session, identifier: str, project_id: int) -> Proposal | None:
-    """Look up proposal by numeric id or propose_code within a project."""
-    try:
-        pid = int(identifier)
-        q = db.query(Proposal).filter(Proposal.id == pid, Proposal.project_id == project_id)
-        p = q.first()
-        if p:
-            return p
-    except (ValueError, TypeError):
-        pass
+def _find_proposal(db: Session, proposal_code: str, project_id: int) -> Proposal | None:
+    """Look up proposal by propose_code within a project."""
     return (
         db.query(Proposal)
-        .filter(Proposal.propose_code == str(identifier), Proposal.project_id == project_id)
+        .filter(Proposal.propose_code == str(proposal_code), Proposal.project_id == project_id)
         .first()
     )
 
 
-def _find_essential(db: Session, identifier: str, proposal_id: int) -> Essential | None:
-    """Look up essential by numeric id or essential_code within a proposal."""
-    try:
-        eid = int(identifier)
-        e = (
-            db.query(Essential)
-            .filter(Essential.id == eid, Essential.proposal_id == proposal_id)
-            .first()
-        )
-        if e:
-            return e
-    except (ValueError, TypeError):
-        pass
+def _find_essential(db: Session, essential_code: str, proposal_id: int) -> Essential | None:
+    """Look up essential by essential_code within a proposal."""
     return (
         db.query(Essential)
-        .filter(Essential.essential_code == str(identifier), Essential.proposal_id == proposal_id)
+        .filter(Essential.essential_code == str(essential_code), Essential.proposal_id == proposal_id)
         .first()
     )
 
@@ -108,12 +82,11 @@ def _can_edit_proposal(db: Session, user_id: int, proposal: Proposal) -> bool:
     return False
 
 
-def _serialize_essential(e: Essential) -> dict:
+def _serialize_essential(e: Essential, proposal_code: str | None) -> dict:
     """Return a dict matching EssentialResponse."""
     return {
-        "id": e.id,
         "essential_code": e.essential_code,
-        "proposal_id": e.proposal_id,
+        "proposal_code": proposal_code,
         "type": e.type.value if hasattr(e.type, "value") else e.type,
         "title": e.title,
         "description": e.description,
@@ -129,18 +102,18 @@ def _serialize_essential(e: Essential) -> dict:
 
 @router.get("", response_model=List[EssentialResponse])
 def list_essentials(
-    project_id: str,
-    proposal_id: str,
+    project_code: str,
+    proposal_code: str,
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
 ):
     """List all Essentials under a Proposal."""
-    project = _find_project(db, project_id)
+    project = _find_project(db, project_code)
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
     check_project_role(db, current_user.id, project.id, min_role="viewer")
 
-    proposal = _find_proposal(db, proposal_id, project.id)
+    proposal = _find_proposal(db, proposal_code, project.id)
     if not proposal:
         raise HTTPException(status_code=404, detail="Proposal not found")
 
@@ -150,24 +123,24 @@ def list_essentials(
         .order_by(Essential.id.asc())
         .all()
     )
-    return [_serialize_essential(e) for e in essentials]
+    return [_serialize_essential(e, proposal.propose_code) for e in essentials]
 
 
 @router.post("", response_model=EssentialResponse, status_code=status.HTTP_201_CREATED)
 def create_essential(
-    project_id: str,
-    proposal_id: str,
+    project_code: str,
+    proposal_code: str,
     body: EssentialCreate,
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
 ):
     """Create a new Essential under an open Proposal."""
-    project = _find_project(db, project_id)
+    project = _find_project(db, project_code)
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
     check_project_role(db, current_user.id, project.id, min_role="dev")
 
-    proposal = _find_proposal(db, proposal_id, project.id)
+    proposal = _find_proposal(db, proposal_code, project.id)
     if not proposal:
         raise HTTPException(status_code=404, detail="Proposal not found")
 
@@ -196,50 +169,50 @@ def create_essential(
         details={"title": essential.title, "type": body.type.value, "proposal_id": proposal.id},
     )
 
-    return _serialize_essential(essential)
+    return _serialize_essential(essential, proposal.propose_code)
 
 
 @router.get("/{essential_id}", response_model=EssentialResponse)
 def get_essential(
-    project_id: str,
-    proposal_id: str,
-    essential_id: str,
+    project_code: str,
+    proposal_code: str,
+    essential_code: str,
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
 ):
-    """Get a single Essential by id or essential_code."""
-    project = _find_project(db, project_id)
+    """Get a single Essential by essential_code."""
+    project = _find_project(db, project_code)
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
     check_project_role(db, current_user.id, project.id, min_role="viewer")
 
-    proposal = _find_proposal(db, proposal_id, project.id)
+    proposal = _find_proposal(db, proposal_code, project.id)
     if not proposal:
         raise HTTPException(status_code=404, detail="Proposal not found")
 
-    essential = _find_essential(db, essential_id, proposal.id)
+    essential = _find_essential(db, essential_code, proposal.id)
     if not essential:
         raise HTTPException(status_code=404, detail="Essential not found")
 
-    return _serialize_essential(essential)
+    return _serialize_essential(essential, proposal.propose_code)
 
 
 @router.patch("/{essential_id}", response_model=EssentialResponse)
 def update_essential(
-    project_id: str,
-    proposal_id: str,
-    essential_id: str,
+    project_code: str,
+    proposal_code: str,
+    essential_code: str,
     body: EssentialUpdate,
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
 ):
     """Update an Essential (only on open Proposals)."""
-    project = _find_project(db, project_id)
+    project = _find_project(db, project_code)
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
     check_project_role(db, current_user.id, project.id, min_role="dev")
 
-    proposal = _find_proposal(db, proposal_id, project.id)
+    proposal = _find_proposal(db, proposal_code, project.id)
     if not proposal:
         raise HTTPException(status_code=404, detail="Proposal not found")
 
@@ -248,7 +221,7 @@ def update_essential(
     if not _can_edit_proposal(db, current_user.id, proposal):
         raise HTTPException(status_code=403, detail="Permission denied")
 
-    essential = _find_essential(db, essential_id, proposal.id)
+    essential = _find_essential(db, essential_code, proposal.id)
     if not essential:
         raise HTTPException(status_code=404, detail="Essential not found")
 
@@ -265,24 +238,24 @@ def update_essential(
         details=data,
     )
 
-    return _serialize_essential(essential)
+    return _serialize_essential(essential, proposal.propose_code)
 
 
 @router.delete("/{essential_id}", status_code=status.HTTP_204_NO_CONTENT)
 def delete_essential(
-    project_id: str,
-    proposal_id: str,
-    essential_id: str,
+    project_code: str,
+    proposal_code: str,
+    essential_code: str,
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
 ):
     """Delete an Essential (only on open Proposals)."""
-    project = _find_project(db, project_id)
+    project = _find_project(db, project_code)
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
     check_project_role(db, current_user.id, project.id, min_role="dev")
 
-    proposal = _find_proposal(db, proposal_id, project.id)
+    proposal = _find_proposal(db, proposal_code, project.id)
     if not proposal:
         raise HTTPException(status_code=404, detail="Proposal not found")
 
@@ -291,7 +264,7 @@ def delete_essential(
     if not _can_edit_proposal(db, current_user.id, proposal):
         raise HTTPException(status_code=403, detail="Permission denied")
 
-    essential = _find_essential(db, essential_id, proposal.id)
+    essential = _find_essential(db, essential_code, proposal.id)
     if not essential:
         raise HTTPException(status_code=404, detail="Essential not found")
 
diff --git a/app/api/routers/meetings.py b/app/api/routers/meetings.py
index 27b13bd..95a5541 100644
--- a/app/api/routers/meetings.py
+++ b/app/api/routers/meetings.py
@@ -18,15 +18,8 @@ router = APIRouter(tags=["Meetings"])
 
 # ---- helpers ----
 
-def _find_meeting_by_id_or_code(db: Session, identifier: str) -> Meeting | None:
-    try:
-        mid = int(identifier)
-        meeting = db.query(Meeting).filter(Meeting.id == mid).first()
-        if meeting:
-            return meeting
-    except (ValueError, TypeError):
-        pass
-    return db.query(Meeting).filter(Meeting.meeting_code == str(identifier)).first()
+def _find_meeting_by_code(db: Session, meeting_code: str) -> Meeting | None:
+    return db.query(Meeting).filter(Meeting.meeting_code == str(meeting_code)).first()
 
 
 def _resolve_project_id(db: Session, project_code: str | None) -> int | None:
@@ -64,16 +57,13 @@ def _serialize_meeting(db: Session, meeting: Meeting) -> dict:
     project = db.query(models.Project).filter(models.Project.id == meeting.project_id).first()
     milestone = db.query(Milestone).filter(Milestone.id == meeting.milestone_id).first()
     return {
-        "id": meeting.id,
         "code": meeting.meeting_code,
         "meeting_code": meeting.meeting_code,
         "title": meeting.title,
         "description": meeting.description,
         "status": meeting.status.value if hasattr(meeting.status, "value") else meeting.status,
         "priority": meeting.priority.value if hasattr(meeting.priority, "value") else meeting.priority,
-        "project_id": meeting.project_id,
         "project_code": project.project_code if project else None,
-        "milestone_id": meeting.milestone_id,
         "milestone_code": milestone.milestone_code if milestone else None,
         "reporter_id": meeting.reporter_id,
         "meeting_time": meeting.scheduled_at.isoformat() if meeting.scheduled_at else None,
@@ -155,6 +145,7 @@ def create_meeting(
 @router.get("/meetings")
 def list_meetings(
     project: str = None,
+    project_code: str = None,
     status_value: str = Query(None, alias="status"),
     order_by: str = None,
     page: int = 1,
@@ -163,8 +154,9 @@ def list_meetings(
 ):
     query = db.query(Meeting)
 
-    if project:
-        project_id = _resolve_project_id(db, project)
+    effective_project = project_code or project
+    if effective_project:
+        project_id = _resolve_project_id(db, effective_project)
         if project_id:
             query = query.filter(Meeting.project_id == project_id)
 
@@ -197,9 +189,9 @@ def list_meetings(
     }
 
 
-@router.get("/meetings/{meeting_id}")
-def get_meeting(meeting_id: str, db: Session = Depends(get_db)):
-    meeting = _find_meeting_by_id_or_code(db, meeting_id)
+@router.get("/meetings/{meeting_code}")
+def get_meeting(meeting_code: str, db: Session = Depends(get_db)):
+    meeting = _find_meeting_by_code(db, meeting_code)
     if not meeting:
         raise HTTPException(status_code=404, detail="Meeting not found")
     return _serialize_meeting(db, meeting)
@@ -213,14 +205,14 @@ class MeetingUpdateBody(BaseModel):
     duration_minutes: Optional[int] = None
 
 
-@router.patch("/meetings/{meeting_id}")
+@router.patch("/meetings/{meeting_code}")
 def update_meeting(
-    meeting_id: str,
+    meeting_code: str,
     body: MeetingUpdateBody,
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
 ):
-    meeting = _find_meeting_by_id_or_code(db, meeting_id)
+    meeting = _find_meeting_by_code(db, meeting_code)
     if not meeting:
         raise HTTPException(status_code=404, detail="Meeting not found")
     check_project_role(db, current_user.id, meeting.project_id, min_role="dev")
@@ -248,13 +240,13 @@ def update_meeting(
     return _serialize_meeting(db, meeting)
 
 
-@router.delete("/meetings/{meeting_id}", status_code=status.HTTP_204_NO_CONTENT)
+@router.delete("/meetings/{meeting_code}", status_code=status.HTTP_204_NO_CONTENT)
 def delete_meeting(
-    meeting_id: str,
+    meeting_code: str,
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
 ):
-    meeting = _find_meeting_by_id_or_code(db, meeting_id)
+    meeting = _find_meeting_by_code(db, meeting_code)
     if not meeting:
         raise HTTPException(status_code=404, detail="Meeting not found")
     check_project_role(db, current_user.id, meeting.project_id, min_role="dev")
@@ -265,13 +257,13 @@ def delete_meeting(
 
 # ---- Attend ----
 
-@router.post("/meetings/{meeting_id}/attend")
+@router.post("/meetings/{meeting_code}/attend")
 def attend_meeting(
-    meeting_id: str,
+    meeting_code: str,
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
 ):
-    meeting = _find_meeting_by_id_or_code(db, meeting_id)
+    meeting = _find_meeting_by_code(db, meeting_code)
     if not meeting:
         raise HTTPException(status_code=404, detail="Meeting not found")
     check_project_role(db, current_user.id, meeting.project_id, min_role="viewer")
diff --git a/app/api/routers/milestone_actions.py b/app/api/routers/milestone_actions.py
index cbe0f49..1c69fb2 100644
--- a/app/api/routers/milestone_actions.py
+++ b/app/api/routers/milestone_actions.py
@@ -20,7 +20,7 @@ from app.services.activity import log_activity
 from app.services.dependency_check import check_milestone_deps
 
 router = APIRouter(
-    prefix="/projects/{project_id}/milestones/{milestone_id}/actions",
+    prefix="/projects/{project_code}/milestones/{milestone_code}/actions",
     tags=["Milestone Actions"],
 )
 
@@ -29,10 +29,18 @@ router = APIRouter(
 # Helpers
 # ---------------------------------------------------------------------------
 
-def _get_milestone_or_404(db: Session, project_id: int, milestone_id: int) -> Milestone:
+def _resolve_project_or_404(db: Session, project_code: str):
+    project = db.query(models.Project).filter(models.Project.project_code == project_code).first()
+    if not project:
+        raise HTTPException(status_code=404, detail="Project not found")
+    return project
+
+
+def _get_milestone_or_404(db: Session, project_code: str, milestone_code: str) -> Milestone:
+    project = _resolve_project_or_404(db, project_code)
     ms = (
         db.query(Milestone)
-        .filter(Milestone.id == milestone_id, Milestone.project_id == project_id)
+        .filter(Milestone.milestone_code == milestone_code, Milestone.project_id == project.id)
         .first()
     )
     if not ms:
@@ -59,8 +67,8 @@ class CloseBody(BaseModel):
 
 @router.get("/preflight", status_code=200)
 def preflight_milestone_actions(
-    project_id: int,
-    milestone_id: int,
+    project_code: str,
+    milestone_code: str,
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
 ):
@@ -69,8 +77,9 @@ def preflight_milestone_actions(
     The frontend uses this to decide whether to *disable* buttons and what
     hint text to show.  This endpoint never mutates data.
     """
-    check_project_role(db, current_user.id, project_id, min_role="viewer")
-    ms = _get_milestone_or_404(db, project_id, milestone_id)
+    project = _resolve_project_or_404(db, project_code)
+    check_project_role(db, current_user.id, project.id, min_role="viewer")
+    ms = _get_milestone_or_404(db, project_code, milestone_code)
     ms_status = _ms_status_value(ms)
 
     result: dict = {"status": ms_status, "freeze": None, "start": None}
@@ -80,7 +89,7 @@ def preflight_milestone_actions(
         release_tasks = (
             db.query(Task)
             .filter(
-                Task.milestone_id == milestone_id,
+                Task.milestone_id == ms.id,
                 Task.task_type == "maintenance",
                 Task.task_subtype == "release",
             )
@@ -118,8 +127,8 @@ def preflight_milestone_actions(
 
 @router.post("/freeze", status_code=200)
 def freeze_milestone(
-    project_id: int,
-    milestone_id: int,
+    project_code: str,
+    milestone_code: str,
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
 ):
@@ -130,10 +139,11 @@ def freeze_milestone(
     - Milestone must have **exactly one** maintenance task with subtype ``release``.
     - Caller must have ``freeze milestone`` permission.
     """
-    check_project_role(db, current_user.id, project_id, min_role="mgr")
-    check_permission(db, current_user.id, project_id, "milestone.freeze")
+    project = _resolve_project_or_404(db, project_code)
+    check_project_role(db, current_user.id, project.id, min_role="mgr")
+    check_permission(db, current_user.id, project.id, "milestone.freeze")
 
-    ms = _get_milestone_or_404(db, project_id, milestone_id)
+    ms = _get_milestone_or_404(db, project_code, milestone_code)
 
     if _ms_status_value(ms) != "open":
         raise HTTPException(
@@ -145,7 +155,7 @@ def freeze_milestone(
     release_tasks = (
         db.query(Task)
         .filter(
-            Task.milestone_id == milestone_id,
+            Task.milestone_id == ms.id,
             Task.task_type == "maintenance",
             Task.task_subtype == "release",
         )
@@ -184,8 +194,8 @@ def freeze_milestone(
 
 @router.post("/start", status_code=200)
 def start_milestone(
-    project_id: int,
-    milestone_id: int,
+    project_code: str,
+    milestone_code: str,
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
 ):
@@ -196,10 +206,11 @@ def start_milestone(
     - All milestone dependencies must be completed.
     - Caller must have ``start milestone`` permission.
     """
-    check_project_role(db, current_user.id, project_id, min_role="mgr")
-    check_permission(db, current_user.id, project_id, "milestone.start")
+    project = _resolve_project_or_404(db, project_code)
+    check_project_role(db, current_user.id, project.id, min_role="mgr")
+    check_permission(db, current_user.id, project.id, "milestone.start")
 
-    ms = _get_milestone_or_404(db, project_id, milestone_id)
+    ms = _get_milestone_or_404(db, project_code, milestone_code)
 
     if _ms_status_value(ms) != "freeze":
         raise HTTPException(
@@ -240,8 +251,8 @@ def start_milestone(
 
 @router.post("/close", status_code=200)
 def close_milestone(
-    project_id: int,
-    milestone_id: int,
+    project_code: str,
+    milestone_code: str,
     body: CloseBody = CloseBody(),
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
@@ -252,10 +263,11 @@ def close_milestone(
     - Milestone must be in ``open``, ``freeze``, or ``undergoing`` status.
     - Caller must have ``close milestone`` permission.
     """
-    check_project_role(db, current_user.id, project_id, min_role="mgr")
-    check_permission(db, current_user.id, project_id, "milestone.close")
+    project = _resolve_project_or_404(db, project_code)
+    check_project_role(db, current_user.id, project.id, min_role="mgr")
+    check_permission(db, current_user.id, project.id, "milestone.close")
 
-    ms = _get_milestone_or_404(db, project_id, milestone_id)
+    ms = _get_milestone_or_404(db, project_code, milestone_code)
     current = _ms_status_value(ms)
 
     allowed_from = {"open", "freeze", "undergoing"}
diff --git a/app/api/routers/milestones.py b/app/api/routers/milestones.py
index 1b4c973..3eeafd7 100644
--- a/app/api/routers/milestones.py
+++ b/app/api/routers/milestones.py
@@ -48,10 +48,10 @@ def _find_milestone(db, identifier, project_id: int = None) -> Milestone | None:
     return q.first()
 
 
-def _serialize_milestone(milestone):
-    """Serialize milestone with JSON fields and code."""
+def _serialize_milestone(db, milestone):
+    """Serialize milestone with JSON fields and code-first identifiers."""
+    project = db.query(models.Project).filter(models.Project.id == milestone.project_id).first()
     return {
-        "id": milestone.id,
         "title": milestone.title,
         "description": milestone.description,
         "status": milestone.status.value if hasattr(milestone.status, 'value') else milestone.status,
@@ -59,9 +59,9 @@ def _serialize_milestone(milestone):
         "planned_release_date": milestone.planned_release_date,
         "depend_on_milestones": json.loads(milestone.depend_on_milestones) if milestone.depend_on_milestones else [],
         "depend_on_tasks": json.loads(milestone.depend_on_tasks) if milestone.depend_on_tasks else [],
-        "project_id": milestone.project_id,
         "milestone_code": milestone.milestone_code,
         "code": milestone.milestone_code,
+        "project_code": project.project_code if project else None,
         "created_by_id": milestone.created_by_id,
         "started_at": milestone.started_at,
         "created_at": milestone.created_at,
@@ -76,7 +76,7 @@ def list_milestones(project_id: str, db: Session = Depends(get_db), current_user
         raise HTTPException(status_code=404, detail="Project not found")
     check_project_role(db, current_user.id, project.id, min_role="viewer")
     milestones = db.query(Milestone).filter(Milestone.project_id == project.id).all()
-    return [_serialize_milestone(m) for m in milestones]
+    return [_serialize_milestone(db, m) for m in milestones]
 
 
 @router.post("", response_model=schemas.MilestoneResponse, status_code=status.HTTP_201_CREATED)
@@ -101,7 +101,7 @@ def create_milestone(project_id: str, milestone: schemas.MilestoneCreate, db: Se
     db.add(db_milestone)
     db.commit()
     db.refresh(db_milestone)
-    return _serialize_milestone(db_milestone)
+    return _serialize_milestone(db, db_milestone)
 
 
 @router.get("/{milestone_id}", response_model=schemas.MilestoneResponse)
@@ -113,7 +113,7 @@ def get_milestone(project_id: str, milestone_id: str, db: Session = Depends(get_
     milestone = _find_milestone(db, milestone_id, project.id)
     if not milestone:
         raise HTTPException(status_code=404, detail="Milestone not found")
-    return _serialize_milestone(milestone)
+    return _serialize_milestone(db, milestone)
 
 
 @router.patch("/{milestone_id}", response_model=schemas.MilestoneResponse)
@@ -163,7 +163,7 @@ def update_milestone(project_id: str, milestone_id: str, milestone: schemas.Mile
         setattr(db_milestone, key, value)
     db.commit()
     db.refresh(db_milestone)
-    return _serialize_milestone(db_milestone)
+    return _serialize_milestone(db, db_milestone)
 
 
 @router.delete("/{milestone_id}", status_code=status.HTTP_204_NO_CONTENT)
diff --git a/app/api/routers/misc.py b/app/api/routers/misc.py
index f201610..0040d3e 100644
--- a/app/api/routers/misc.py
+++ b/app/api/routers/misc.py
@@ -149,18 +149,19 @@ def create_milestone(ms: schemas.MilestoneCreate, db: Session = Depends(get_db),
 
 
 @router.get("/milestones", response_model=List[schemas.MilestoneResponse], tags=["Milestones"])
-def list_milestones(project_id: str = None, status_filter: str = None, db: Session = Depends(get_db)):
+def list_milestones(project_id: str = None, project_code: str = None, status_filter: str = None, db: Session = Depends(get_db)):
     query = db.query(MilestoneModel)
-    if project_id:
+    effective_project = project_code or project_id
+    if effective_project:
         # Resolve project_id by numeric id or project_code
         resolved_project = None
         try:
-            pid = int(project_id)
+            pid = int(effective_project)
             resolved_project = db.query(models.Project).filter(models.Project.id == pid).first()
         except (ValueError, TypeError):
             pass
         if not resolved_project:
-            resolved_project = db.query(models.Project).filter(models.Project.project_code == project_id).first()
+            resolved_project = db.query(models.Project).filter(models.Project.project_code == effective_project).first()
         if not resolved_project:
             raise HTTPException(status_code=404, detail="Project not found")
         query = query.filter(MilestoneModel.project_id == resolved_project.id)
@@ -428,14 +429,21 @@ def dashboard_stats(project_id: int = None, db: Session = Depends(get_db)):
 # ============ Milestone-scoped Tasks ============
 
 @router.get("/tasks/{project_code}/{milestone_id}", tags=["Tasks"])
-def list_milestone_tasks(project_code: str, milestone_id: int, db: Session = Depends(get_db)):
+def list_milestone_tasks(project_code: str, milestone_id: str, db: Session = Depends(get_db)):
     project = db.query(models.Project).filter(models.Project.project_code == project_code).first()
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
     
+    milestone = db.query(MilestoneModel).filter(
+        MilestoneModel.milestone_code == milestone_id,
+        MilestoneModel.project_id == project.id,
+    ).first()
+    if not milestone:
+        raise HTTPException(status_code=404, detail="Milestone not found")
+
     tasks = db.query(Task).filter(
         Task.project_id == project.id,
-        Task.milestone_id == milestone_id
+        Task.milestone_id == milestone.id
     ).all()
     
     return [{
@@ -459,12 +467,12 @@ def list_milestone_tasks(project_code: str, milestone_id: int, db: Session = Dep
 
 
 @router.post("/tasks/{project_code}/{milestone_id}", status_code=status.HTTP_201_CREATED, tags=["Tasks"])
-def create_milestone_task(project_code: str, milestone_id: int, task_data: dict, db: Session = Depends(get_db), current_user: models.User = Depends(get_current_user_or_apikey)):
+def create_milestone_task(project_code: str, milestone_id: str, task_data: dict, db: Session = Depends(get_db), current_user: models.User = Depends(get_current_user_or_apikey)):
     project = db.query(models.Project).filter(models.Project.project_code == project_code).first()
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
     
-    ms = db.query(MilestoneModel).filter(MilestoneModel.id == milestone_id).first()
+    ms = db.query(MilestoneModel).filter(MilestoneModel.milestone_code == milestone_id, MilestoneModel.project_id == project.id).first()
     if not ms:
         raise HTTPException(status_code=404, detail="Milestone not found")
     
@@ -491,7 +499,7 @@ def create_milestone_task(project_code: str, milestone_id: int, task_data: dict,
         task_type=task_data.get("task_type", "issue"),  # P7.1: default changed from 'task' to 'issue'
         task_subtype=task_data.get("task_subtype"),
         project_id=project.id,
-        milestone_id=milestone_id,
+        milestone_id=ms.id,
         reporter_id=current_user.id,
         task_code=task_code,
         estimated_effort=task_data.get("estimated_effort"),
@@ -503,10 +511,10 @@ def create_milestone_task(project_code: str, milestone_id: int, task_data: dict,
     db.refresh(task)
     
     return {
-        "id": task.id,
         "title": task.title,
         "description": task.description,
         "task_code": task.task_code,
+        "code": task.task_code,
         "status": task.status.value,
         "priority": task.priority.value,
         "created_at": task.created_at,
@@ -516,15 +524,8 @@ def create_milestone_task(project_code: str, milestone_id: int, task_data: dict,
 # ============ Supports ============
 
 
-def _find_support_by_id_or_code(db: Session, identifier: str) -> Support | None:
-    try:
-        support_id = int(identifier)
-        support = db.query(Support).filter(Support.id == support_id).first()
-        if support:
-            return support
-    except (TypeError, ValueError):
-        pass
-    return db.query(Support).filter(Support.support_code == str(identifier)).first()
+def _find_support_by_code(db: Session, support_code: str) -> Support | None:
+    return db.query(Support).filter(Support.support_code == str(support_code)).first()
 
 
 
@@ -536,16 +537,13 @@ def _serialize_support(db: Session, support: Support) -> dict:
         assignee = db.query(models.User).filter(models.User.id == support.assignee_id).first()
 
     return {
-        "id": support.id,
         "code": support.support_code,
         "support_code": support.support_code,
         "title": support.title,
         "description": support.description,
         "status": support.status.value if hasattr(support.status, "value") else support.status,
         "priority": support.priority.value if hasattr(support.priority, "value") else support.priority,
-        "project_id": support.project_id,
         "project_code": project.project_code if project else None,
-        "milestone_id": support.milestone_id,
         "milestone_code": milestone.milestone_code if milestone else None,
         "reporter_id": support.reporter_id,
         "assignee_id": support.assignee_id,
@@ -585,26 +583,30 @@ def list_all_supports(
 
 
 @router.get("/supports/{project_code}/{milestone_id}", tags=["Supports"])
-def list_supports(project_code: str, milestone_id: int, db: Session = Depends(get_db)):
+def list_supports(project_code: str, milestone_id: str, db: Session = Depends(get_db)):
     project = db.query(models.Project).filter(models.Project.project_code == project_code).first()
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
 
+    milestone = db.query(MilestoneModel).filter(MilestoneModel.milestone_code == milestone_id, MilestoneModel.project_id == project.id).first()
+    if not milestone:
+        raise HTTPException(status_code=404, detail="Milestone not found")
+
     supports = db.query(Support).filter(
         Support.project_id == project.id,
-        Support.milestone_id == milestone_id
+        Support.milestone_id == milestone.id
     ).all()
 
     return [_serialize_support(db, s) for s in supports]
 
 
 @router.post("/supports/{project_code}/{milestone_id}", status_code=status.HTTP_201_CREATED, tags=["Supports"])
-def create_support(project_code: str, milestone_id: int, support_data: dict, db: Session = Depends(get_db), current_user: models.User = Depends(get_current_user_or_apikey)):
+def create_support(project_code: str, milestone_id: str, support_data: dict, db: Session = Depends(get_db), current_user: models.User = Depends(get_current_user_or_apikey)):
     project = db.query(models.Project).filter(models.Project.project_code == project_code).first()
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
 
-    ms = db.query(MilestoneModel).filter(MilestoneModel.id == milestone_id).first()
+    ms = db.query(MilestoneModel).filter(MilestoneModel.milestone_code == milestone_id, MilestoneModel.project_id == project.id).first()
     if not ms:
         raise HTTPException(status_code=404, detail="Milestone not found")
 
@@ -612,7 +614,7 @@ def create_support(project_code: str, milestone_id: int, support_data: dict, db:
         raise HTTPException(status_code=400, detail="Cannot add items to a milestone that is undergoing")
 
     milestone_code = ms.milestone_code or f"m{ms.id}"
-    max_support = db.query(Support).filter(Support.milestone_id == milestone_id).order_by(Support.id.desc()).first()
+    max_support = db.query(Support).filter(Support.milestone_id == ms.id).order_by(Support.id.desc()).first()
     next_num = (max_support.id + 1) if max_support else 1
     support_code = f"{milestone_code}:S{next_num:05x}"
 
@@ -622,7 +624,7 @@ def create_support(project_code: str, milestone_id: int, support_data: dict, db:
         status=SupportStatus.OPEN,
         priority=SupportPriority.MEDIUM,
         project_id=project.id,
-        milestone_id=milestone_id,
+        milestone_id=ms.id,
         reporter_id=current_user.id,
         support_code=support_code,
     )
@@ -632,18 +634,18 @@ def create_support(project_code: str, milestone_id: int, support_data: dict, db:
     return _serialize_support(db, support)
 
 
-@router.get("/supports/{support_id}", tags=["Supports"])
-def get_support(support_id: str, db: Session = Depends(get_db), current_user: models.User = Depends(get_current_user_or_apikey)):
-    support = _find_support_by_id_or_code(db, support_id)
+@router.get("/supports/{support_code}", tags=["Supports"])
+def get_support(support_code: str, db: Session = Depends(get_db), current_user: models.User = Depends(get_current_user_or_apikey)):
+    support = _find_support_by_code(db, support_code)
     if not support:
         raise HTTPException(status_code=404, detail="Support not found")
     check_project_role(db, current_user.id, support.project_id, min_role="viewer")
     return _serialize_support(db, support)
 
 
-@router.patch("/supports/{support_id}", tags=["Supports"])
-def update_support(support_id: str, support_data: dict, db: Session = Depends(get_db), current_user: models.User = Depends(get_current_user_or_apikey)):
-    support = _find_support_by_id_or_code(db, support_id)
+@router.patch("/supports/{support_code}", tags=["Supports"])
+def update_support(support_code: str, support_data: dict, db: Session = Depends(get_db), current_user: models.User = Depends(get_current_user_or_apikey)):
+    support = _find_support_by_code(db, support_code)
     if not support:
         raise HTTPException(status_code=404, detail="Support not found")
     check_project_role(db, current_user.id, support.project_id, min_role="dev")
@@ -668,9 +670,9 @@ def update_support(support_id: str, support_data: dict, db: Session = Depends(ge
     return _serialize_support(db, support)
 
 
-@router.delete("/supports/{support_id}", status_code=status.HTTP_204_NO_CONTENT, tags=["Supports"])
-def delete_support(support_id: str, db: Session = Depends(get_db), current_user: models.User = Depends(get_current_user_or_apikey)):
-    support = _find_support_by_id_or_code(db, support_id)
+@router.delete("/supports/{support_code}", status_code=status.HTTP_204_NO_CONTENT, tags=["Supports"])
+def delete_support(support_code: str, db: Session = Depends(get_db), current_user: models.User = Depends(get_current_user_or_apikey)):
+    support = _find_support_by_code(db, support_code)
     if not support:
         raise HTTPException(status_code=404, detail="Support not found")
     check_project_role(db, current_user.id, support.project_id, min_role="dev")
@@ -679,9 +681,9 @@ def delete_support(support_id: str, db: Session = Depends(get_db), current_user:
     return None
 
 
-@router.post("/supports/{support_id}/take", tags=["Supports"])
-def take_support(support_id: str, db: Session = Depends(get_db), current_user: models.User = Depends(get_current_user_or_apikey)):
-    support = _find_support_by_id_or_code(db, support_id)
+@router.post("/supports/{support_code}/take", tags=["Supports"])
+def take_support(support_code: str, db: Session = Depends(get_db), current_user: models.User = Depends(get_current_user_or_apikey)):
+    support = _find_support_by_code(db, support_code)
     if not support:
         raise HTTPException(status_code=404, detail="Support not found")
     check_project_role(db, current_user.id, support.project_id, min_role="dev")
@@ -697,9 +699,9 @@ def take_support(support_id: str, db: Session = Depends(get_db), current_user: m
     return _serialize_support(db, support)
 
 
-@router.post("/supports/{support_id}/transition", tags=["Supports"])
-def transition_support(support_id: str, support_data: dict, db: Session = Depends(get_db), current_user: models.User = Depends(get_current_user_or_apikey)):
-    support = _find_support_by_id_or_code(db, support_id)
+@router.post("/supports/{support_code}/transition", tags=["Supports"])
+def transition_support(support_code: str, support_data: dict, db: Session = Depends(get_db), current_user: models.User = Depends(get_current_user_or_apikey)):
+    support = _find_support_by_code(db, support_code)
     if not support:
         raise HTTPException(status_code=404, detail="Support not found")
     check_project_role(db, current_user.id, support.project_id, min_role="dev")
@@ -717,20 +719,25 @@ def transition_support(support_id: str, support_data: dict, db: Session = Depend
 # ============ Meetings ============
 
 @router.get("/meetings/{project_code}/{milestone_id}", tags=["Meetings"])
-def list_meetings(project_code: str, milestone_id: int, db: Session = Depends(get_db)):
+def list_meetings(project_code: str, milestone_id: str, db: Session = Depends(get_db)):
     project = db.query(models.Project).filter(models.Project.project_code == project_code).first()
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
     
+    milestone = db.query(MilestoneModel).filter(MilestoneModel.milestone_code == milestone_id, MilestoneModel.project_id == project.id).first()
+    if not milestone:
+        raise HTTPException(status_code=404, detail="Milestone not found")
+
     meetings = db.query(Meeting).filter(
         Meeting.project_id == project.id,
-        Meeting.milestone_id == milestone_id
+        Meeting.milestone_id == milestone.id
     ).all()
     
     return [{
-        "id": m.id,
         "title": m.title,
         "description": m.description,
+        "meeting_code": m.meeting_code,
+        "code": m.meeting_code,
         "status": m.status.value,
         "priority": m.priority.value,
         "scheduled_at": m.scheduled_at,
@@ -740,12 +747,12 @@ def list_meetings(project_code: str, milestone_id: int, db: Session = Depends(ge
 
 
 @router.post("/meetings/{project_code}/{milestone_id}", status_code=status.HTTP_201_CREATED, tags=["Meetings"])
-def create_meeting(project_code: str, milestone_id: int, meeting_data: dict, db: Session = Depends(get_db), current_user: models.User = Depends(get_current_user_or_apikey)):
+def create_meeting(project_code: str, milestone_id: str, meeting_data: dict, db: Session = Depends(get_db), current_user: models.User = Depends(get_current_user_or_apikey)):
     project = db.query(models.Project).filter(models.Project.project_code == project_code).first()
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
     
-    ms = db.query(MilestoneModel).filter(MilestoneModel.id == milestone_id).first()
+    ms = db.query(MilestoneModel).filter(MilestoneModel.milestone_code == milestone_id, MilestoneModel.project_id == project.id).first()
     if not ms:
         raise HTTPException(status_code=404, detail="Milestone not found")
     
@@ -753,7 +760,7 @@ def create_meeting(project_code: str, milestone_id: int, meeting_data: dict, db:
         raise HTTPException(status_code=400, detail="Cannot add items to a milestone that is undergoing")
     
     milestone_code = ms.milestone_code or f"m{ms.id}"
-    max_meeting = db.query(Meeting).filter(Meeting.milestone_id == milestone_id).order_by(Meeting.id.desc()).first()
+    max_meeting = db.query(Meeting).filter(Meeting.milestone_id == ms.id).order_by(Meeting.id.desc()).first()
     next_num = (max_meeting.id + 1) if max_meeting else 1
     meeting_code = f"{milestone_code}:M{next_num:05x}"
     
@@ -770,7 +777,7 @@ def create_meeting(project_code: str, milestone_id: int, meeting_data: dict, db:
         status=MeetingStatus.SCHEDULED,
         priority=MeetingPriority.MEDIUM,
         project_id=project.id,
-        milestone_id=milestone_id,
+        milestone_id=ms.id,
         reporter_id=current_user.id,
         meeting_code=meeting_code,
         scheduled_at=scheduled_at,
@@ -779,4 +786,14 @@ def create_meeting(project_code: str, milestone_id: int, meeting_data: dict, db:
     db.add(meeting)
     db.commit()
     db.refresh(meeting)
-    return meeting
+    return {
+        "meeting_code": meeting.meeting_code,
+        "code": meeting.meeting_code,
+        "title": meeting.title,
+        "description": meeting.description,
+        "status": meeting.status.value,
+        "priority": meeting.priority.value,
+        "scheduled_at": meeting.scheduled_at,
+        "duration_minutes": meeting.duration_minutes,
+        "created_at": meeting.created_at,
+    }
diff --git a/app/api/routers/proposals.py b/app/api/routers/proposals.py
index b3ed736..c2dcad1 100644
--- a/app/api/routers/proposals.py
+++ b/app/api/routers/proposals.py
@@ -19,15 +19,14 @@ from app.models.task import Task, TaskStatus, TaskPriority
 from app.schemas import schemas
 from app.services.activity import log_activity
 
-router = APIRouter(prefix="/projects/{project_id}/proposals", tags=["Proposals"])
+router = APIRouter(prefix="/projects/{project_code}/proposals", tags=["Proposals"])
 
 
-def _serialize_essential(e: Essential) -> dict:
+def _serialize_essential(e: Essential, proposal_code: str | None) -> dict:
     """Serialize an Essential for embedding in Proposal detail."""
     return {
-        "id": e.id,
         "essential_code": e.essential_code,
-        "proposal_id": e.proposal_id,
+        "proposal_code": proposal_code,
         "type": e.type.value if hasattr(e.type, "value") else e.type,
         "title": e.title,
         "description": e.description,
@@ -41,14 +40,14 @@ def _serialize_proposal(db: Session, proposal: Proposal, *, include_essentials:
     """Serialize proposal with created_by_username."""
     creator = db.query(models.User).filter(models.User.id == proposal.created_by_id).first() if proposal.created_by_id else None
     code = proposal.propose_code  # DB column; also exposed as proposal_code
+    project = db.query(models.Project).filter(models.Project.id == proposal.project_id).first()
     result = {
-        "id": proposal.id,
         "title": proposal.title,
         "description": proposal.description,
         "proposal_code": code,        # preferred name
         "propose_code": code,         # backward compat
         "status": proposal.status.value if hasattr(proposal.status, "value") else proposal.status,
-        "project_id": proposal.project_id,
+        "project_code": project.project_code if project else None,
         "created_by_id": proposal.created_by_id,
         "created_by_username": creator.username if creator else None,
         "feat_task_id": proposal.feat_task_id,  # DEPRECATED (BE-PR-010): read-only for legacy rows. Clients should use generated_tasks.
@@ -62,7 +61,7 @@ def _serialize_proposal(db: Session, proposal: Proposal, *, include_essentials:
             .order_by(Essential.id.asc())
             .all()
         )
-        result["essentials"] = [_serialize_essential(e) for e in essentials]
+        result["essentials"] = [_serialize_essential(e, code) for e in essentials]
 
         # BE-PR-008: include tasks generated from this Proposal via Accept
         gen_tasks = (
@@ -71,46 +70,34 @@ def _serialize_proposal(db: Session, proposal: Proposal, *, include_essentials:
             .order_by(Task.id.asc())
             .all()
         )
+        def _lookup_essential_code(essential_id: int | None) -> str | None:
+            if not essential_id:
+                return None
+            essential = db.query(Essential).filter(Essential.id == essential_id).first()
+            return essential.essential_code if essential else None
+
         result["generated_tasks"] = [
             {
-                "task_id": t.id,
                 "task_code": t.task_code,
                 "task_type": t.task_type or "story",
                 "task_subtype": t.task_subtype,
                 "title": t.title,
                 "status": t.status.value if hasattr(t.status, "value") else t.status,
-                "source_essential_id": t.source_essential_id,
+                "source_essential_code": _lookup_essential_code(t.source_essential_id),
             }
             for t in gen_tasks
         ]
     return result
 
 
-def _find_project(db, identifier):
-    """Look up project by numeric id or project_code."""
-    try:
-        pid = int(identifier)
-        p = db.query(models.Project).filter(models.Project.id == pid).first()
-        if p:
-            return p
-    except (ValueError, TypeError):
-        pass
-    return db.query(models.Project).filter(models.Project.project_code == str(identifier)).first()
+def _find_project(db, project_code: str):
+    """Look up project by project_code."""
+    return db.query(models.Project).filter(models.Project.project_code == str(project_code)).first()
 
 
-def _find_proposal(db, identifier, project_id: int = None) -> Proposal | None:
-    """Look up proposal by numeric id or propose_code."""
-    try:
-        pid = int(identifier)
-        q = db.query(Proposal).filter(Proposal.id == pid)
-        if project_id:
-            q = q.filter(Proposal.project_id == project_id)
-        p = q.first()
-        if p:
-            return p
-    except (ValueError, TypeError):
-        pass
-    q = db.query(Proposal).filter(Proposal.propose_code == str(identifier))
+def _find_proposal(db, proposal_code: str, project_id: int = None) -> Proposal | None:
+    """Look up proposal by propose_code."""
+    q = db.query(Proposal).filter(Proposal.propose_code == str(proposal_code))
     if project_id:
         q = q.filter(Proposal.project_id == project_id)
     return q.first()
@@ -147,11 +134,11 @@ def _can_edit_proposal(db: Session, user_id: int, proposal: Proposal) -> bool:
 
 @router.get("", response_model=List[schemas.ProposalResponse])
 def list_proposals(
-    project_id: str,
+    project_code: str,
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
 ):
-    project = _find_project(db, project_id)
+    project = _find_project(db, project_code)
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
     check_project_role(db, current_user.id, project.id, min_role="viewer")
@@ -166,12 +153,12 @@ def list_proposals(
 
 @router.post("", response_model=schemas.ProposalResponse, status_code=status.HTTP_201_CREATED)
 def create_proposal(
-    project_id: str,
+    project_code: str,
     proposal_in: schemas.ProposalCreate,
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
 ):
-    project = _find_project(db, project_id)
+    project = _find_project(db, project_code)
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
     check_project_role(db, current_user.id, project.id, min_role="dev")
@@ -197,17 +184,17 @@ def create_proposal(
 
 @router.get("/{proposal_id}", response_model=schemas.ProposalDetailResponse)
 def get_proposal(
-    project_id: str,
-    proposal_id: str,
+    project_code: str,
+    proposal_code: str,
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
 ):
     """Get a single Proposal with its Essentials list embedded."""
-    project = _find_project(db, project_id)
+    project = _find_project(db, project_code)
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
     check_project_role(db, current_user.id, project.id, min_role="viewer")
-    proposal = _find_proposal(db, proposal_id, project.id)
+    proposal = _find_proposal(db, proposal_code, project.id)
     if not proposal:
         raise HTTPException(status_code=404, detail="Proposal not found")
     return _serialize_proposal(db, proposal, include_essentials=True)
@@ -215,16 +202,16 @@ def get_proposal(
 
 @router.patch("/{proposal_id}", response_model=schemas.ProposalResponse)
 def update_proposal(
-    project_id: str,
-    proposal_id: str,
+    project_code: str,
+    proposal_code: str,
     proposal_in: schemas.ProposalUpdate,
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
 ):
-    project = _find_project(db, project_id)
+    project = _find_project(db, project_code)
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
-    proposal = _find_proposal(db, proposal_id, project.id)
+    proposal = _find_proposal(db, proposal_code, project.id)
     if not proposal:
         raise HTTPException(status_code=404, detail="Proposal not found")
 
@@ -253,13 +240,13 @@ def update_proposal(
 # ---- Actions ----
 
 class AcceptRequest(schemas.BaseModel):
-    milestone_id: int
+    milestone_code: str
 
 
 @router.post("/{proposal_id}/accept", response_model=schemas.ProposalAcceptResponse)
 def accept_proposal(
-    project_id: str,
-    proposal_id: str,
+    project_code: str,
+    proposal_code: str,
     body: AcceptRequest,
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
@@ -274,10 +261,10 @@ def accept_proposal(
     All tasks are created in a single transaction.  The Proposal must have at
     least one Essential to be accepted.
     """
-    project = _find_project(db, project_id)
+    project = _find_project(db, project_code)
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
-    proposal = _find_proposal(db, proposal_id, project.id)
+    proposal = _find_proposal(db, proposal_code, project.id)
     if not proposal:
         raise HTTPException(status_code=404, detail="Proposal not found")
 
@@ -289,7 +276,7 @@ def accept_proposal(
 
     # Validate milestone
     milestone = db.query(Milestone).filter(
-        Milestone.id == body.milestone_id,
+        Milestone.milestone_code == body.milestone_code,
         Milestone.project_id == project.id,
     ).first()
     if not milestone:
@@ -355,12 +342,10 @@ def accept_proposal(
         db.flush()  # materialise task.id
 
         generated_tasks.append({
-            "task_id": task.id,
             "task_code": task_code,
             "task_type": "story",
             "task_subtype": task_subtype,
             "title": essential.title,
-            "essential_id": essential.id,
             "essential_code": essential.essential_code,
         })
         next_num = task.id + 1  # use real id for next code to stay consistent
@@ -372,9 +357,9 @@ def accept_proposal(
     db.refresh(proposal)
 
     log_activity(db, "accept", "proposal", proposal.id, user_id=current_user.id, details={
-        "milestone_id": milestone.id,
+        "milestone_code": milestone.milestone_code,
         "generated_tasks": [
-            {"task_id": t["task_id"], "task_code": t["task_code"], "essential_id": t["essential_id"]}
+            {"task_code": t["task_code"], "essential_code": t["essential_code"]}
             for t in generated_tasks
         ],
     })
@@ -390,17 +375,17 @@ class RejectRequest(schemas.BaseModel):
 
 @router.post("/{proposal_id}/reject", response_model=schemas.ProposalResponse)
 def reject_proposal(
-    project_id: str,
-    proposal_id: str,
+    project_code: str,
+    proposal_code: str,
     body: RejectRequest | None = None,
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
 ):
     """Reject a proposal."""
-    project = _find_project(db, project_id)
+    project = _find_project(db, project_code)
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
-    proposal = _find_proposal(db, proposal_id, project.id)
+    proposal = _find_proposal(db, proposal_code, project.id)
     if not proposal:
         raise HTTPException(status_code=404, detail="Proposal not found")
 
@@ -423,16 +408,16 @@ def reject_proposal(
 
 @router.post("/{proposal_id}/reopen", response_model=schemas.ProposalResponse)
 def reopen_proposal(
-    project_id: str,
-    proposal_id: str,
+    project_code: str,
+    proposal_code: str,
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
 ):
     """Reopen a rejected proposal back to open."""
-    project = _find_project(db, project_id)
+    project = _find_project(db, project_code)
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
-    proposal = _find_proposal(db, proposal_id, project.id)
+    proposal = _find_proposal(db, proposal_code, project.id)
     if not proposal:
         raise HTTPException(status_code=404, detail="Proposal not found")
 
diff --git a/app/api/routers/proposes.py b/app/api/routers/proposes.py
index 2d9d42f..be2fac3 100644
--- a/app/api/routers/proposes.py
+++ b/app/api/routers/proposes.py
@@ -28,83 +28,83 @@ from app.api.rbac import check_project_role, check_permission, is_global_admin
 from app.services.activity import log_activity
 
 # Legacy router — same logic, old URL prefix
-router = APIRouter(prefix="/projects/{project_id}/proposes", tags=["Proposes (legacy)"])
+router = APIRouter(prefix="/projects/{project_code}/proposes", tags=["Proposes (legacy)"])
 
 
 @router.get("", response_model=List[schemas.ProposalResponse])
 def list_proposes(
-    project_id: str,
+    project_code: str,
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
 ):
     from app.api.routers.proposals import list_proposals
-    return list_proposals(project_id=project_id, db=db, current_user=current_user)
+    return list_proposals(project_code=project_code, db=db, current_user=current_user)
 
 
 @router.post("", response_model=schemas.ProposalResponse, status_code=status.HTTP_201_CREATED)
 def create_propose(
-    project_id: str,
+    project_code: str,
     proposal_in: schemas.ProposalCreate,
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
 ):
     from app.api.routers.proposals import create_proposal
-    return create_proposal(project_id=project_id, proposal_in=proposal_in, db=db, current_user=current_user)
+    return create_proposal(project_code=project_code, proposal_in=proposal_in, db=db, current_user=current_user)
 
 
 @router.get("/{propose_id}", response_model=schemas.ProposalResponse)
 def get_propose(
-    project_id: str,
+    project_code: str,
     propose_id: str,
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
 ):
     from app.api.routers.proposals import get_proposal
-    return get_proposal(project_id=project_id, proposal_id=propose_id, db=db, current_user=current_user)
+    return get_proposal(project_code=project_code, proposal_code=propose_id, db=db, current_user=current_user)
 
 
 @router.patch("/{propose_id}", response_model=schemas.ProposalResponse)
 def update_propose(
-    project_id: str,
+    project_code: str,
     propose_id: str,
     proposal_in: schemas.ProposalUpdate,
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
 ):
     from app.api.routers.proposals import update_proposal
-    return update_proposal(project_id=project_id, proposal_id=propose_id, proposal_in=proposal_in, db=db, current_user=current_user)
+    return update_proposal(project_code=project_code, proposal_code=propose_id, proposal_in=proposal_in, db=db, current_user=current_user)
 
 
 @router.post("/{propose_id}/accept", response_model=schemas.ProposalResponse)
 def accept_propose(
-    project_id: str,
+    project_code: str,
     propose_id: str,
     body: AcceptRequest,
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
 ):
     from app.api.routers.proposals import accept_proposal
-    return accept_proposal(project_id=project_id, proposal_id=propose_id, body=body, db=db, current_user=current_user)
+    return accept_proposal(project_code=project_code, proposal_code=propose_id, body=body, db=db, current_user=current_user)
 
 
 @router.post("/{propose_id}/reject", response_model=schemas.ProposalResponse)
 def reject_propose(
-    project_id: str,
+    project_code: str,
     propose_id: str,
     body: RejectRequest | None = None,
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
 ):
     from app.api.routers.proposals import reject_proposal
-    return reject_proposal(project_id=project_id, proposal_id=propose_id, body=body, db=db, current_user=current_user)
+    return reject_proposal(project_code=project_code, proposal_code=propose_id, body=body, db=db, current_user=current_user)
 
 
 @router.post("/{propose_id}/reopen", response_model=schemas.ProposalResponse)
 def reopen_propose(
-    project_id: str,
+    project_code: str,
     propose_id: str,
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
 ):
     from app.api.routers.proposals import reopen_proposal
-    return reopen_proposal(project_id=project_id, proposal_id=propose_id, db=db, current_user=current_user)
+    return reopen_proposal(project_code=project_code, proposal_code=propose_id, db=db, current_user=current_user)
diff --git a/app/api/routers/tasks.py b/app/api/routers/tasks.py
index f2c654d..6eeb36b 100644
--- a/app/api/routers/tasks.py
+++ b/app/api/routers/tasks.py
@@ -10,6 +10,8 @@ from app.core.config import get_db
 from app.models import models
 from app.models.task import Task, TaskStatus, TaskPriority
 from app.models.milestone import Milestone
+from app.models.proposal import Proposal
+from app.models.essential import Essential
 from app.schemas import schemas
 from app.services.webhook import fire_webhooks_sync
 from app.models.notification import Notification as NotificationModel
@@ -21,14 +23,9 @@ from app.services.dependency_check import check_task_deps
 router = APIRouter(tags=["Tasks"])
 
 
-def _resolve_task(db: Session, identifier: str) -> Task:
-    """Resolve a task by numeric id or task_code string.
-    Raises 404 if not found."""
-    try:
-        task_id = int(identifier)
-        task = db.query(Task).filter(Task.id == task_id).first()
-    except (ValueError, TypeError):
-        task = db.query(Task).filter(Task.task_code == identifier).first()
+def _resolve_task(db: Session, task_code: str) -> Task:
+    """Resolve a task by task_code string. Raises 404 if not found."""
+    task = db.query(Task).filter(Task.task_code == task_code).first()
     if not task:
         raise HTTPException(status_code=404, detail="Task not found")
     return task
@@ -118,9 +115,7 @@ def _notify_user(db, user_id, ntype, title, message=None, entity_type=None, enti
     return n
 
 
-def _resolve_project_id(db: Session, project_id: int | None, project_code: str | None) -> int | None:
-    if project_id:
-        return project_id
+def _resolve_project_id(db: Session, project_code: str | None) -> int | None:
     if not project_code:
         return None
     project = db.query(models.Project).filter(models.Project.project_code == project_code).first()
@@ -129,40 +124,36 @@ def _resolve_project_id(db: Session, project_id: int | None, project_code: str |
     return project.id
 
 
-def _resolve_milestone(db: Session, milestone_id: int | None, milestone_code: str | None, project_id: int | None) -> Milestone | None:
-    if milestone_id:
-        query = db.query(Milestone).filter(Milestone.id == milestone_id)
-        if project_id:
-            query = query.filter(Milestone.project_id == project_id)
-        milestone = query.first()
-    elif milestone_code:
-        query = db.query(Milestone).filter(Milestone.milestone_code == milestone_code)
-        if project_id:
-            query = query.filter(Milestone.project_id == project_id)
-        milestone = query.first()
-    else:
+def _resolve_milestone(db: Session, milestone_code: str | None, project_id: int | None) -> Milestone | None:
+    if not milestone_code:
         return None
 
+    query = db.query(Milestone).filter(Milestone.milestone_code == milestone_code)
+    if project_id:
+        query = query.filter(Milestone.project_id == project_id)
+    milestone = query.first()
+
     if not milestone:
         raise HTTPException(status_code=404, detail="Milestone not found")
     return milestone
 
 
-def _find_task_by_id_or_code(db: Session, identifier: str) -> Task | None:
-    try:
-        task_id = int(identifier)
-        task = db.query(Task).filter(Task.id == task_id).first()
-        if task:
-            return task
-    except ValueError:
-        pass
-    return db.query(Task).filter(Task.task_code == identifier).first()
+def _find_task_by_code(db: Session, task_code: str) -> Task | None:
+    return db.query(Task).filter(Task.task_code == task_code).first()
 
 
 def _serialize_task(db: Session, task: Task) -> dict:
     payload = schemas.TaskResponse.model_validate(task).model_dump(mode="json")
     project = db.query(models.Project).filter(models.Project.id == task.project_id).first()
     milestone = db.query(Milestone).filter(Milestone.id == task.milestone_id).first()
+    proposal_code = None
+    essential_code = None
+    if task.source_proposal_id:
+        proposal = db.query(Proposal).filter(Proposal.id == task.source_proposal_id).first()
+        proposal_code = proposal.propose_code if proposal else None
+    if task.source_essential_id:
+        essential = db.query(Essential).filter(Essential.id == task.source_essential_id).first()
+        essential_code = essential.essential_code if essential else None
     assignee = None
     if task.assignee_id:
         assignee = db.query(models.User).filter(models.User.id == task.assignee_id).first()
@@ -174,6 +165,8 @@ def _serialize_task(db: Session, task: Task) -> dict:
         "milestone_code": milestone.milestone_code if milestone else None,
         "taken_by": assignee.username if assignee else None,
         "due_date": None,
+        "source_proposal_code": proposal_code,
+        "source_essential_code": essential_code,
     })
     return payload
 
@@ -191,8 +184,8 @@ def create_task(task_in: schemas.TaskCreate, bg: BackgroundTasks, db: Session =
     else:
         data.pop("type", None)
 
-    data["project_id"] = _resolve_project_id(db, data.get("project_id"), data.pop("project_code", None))
-    milestone = _resolve_milestone(db, data.get("milestone_id"), data.pop("milestone_code", None), data.get("project_id"))
+    data["project_id"] = _resolve_project_id(db, data.pop("project_code", None))
+    milestone = _resolve_milestone(db, data.pop("milestone_code", None), data.get("project_id"))
     if milestone:
         data["milestone_id"] = milestone.id
         data["project_id"] = milestone.project_id
@@ -201,17 +194,12 @@ def create_task(task_in: schemas.TaskCreate, bg: BackgroundTasks, db: Session =
     data["created_by_id"] = current_user.id
 
     if not data.get("project_id"):
-        raise HTTPException(status_code=400, detail="project_id or project_code is required")
+        raise HTTPException(status_code=400, detail="project_code is required")
     if not data.get("milestone_id"):
-        raise HTTPException(status_code=400, detail="milestone_id or milestone_code is required")
+        raise HTTPException(status_code=400, detail="milestone_code is required")
 
     check_project_role(db, current_user.id, data["project_id"], min_role="dev")
 
-    if not milestone:
-        milestone = db.query(Milestone).filter(
-            Milestone.id == data["milestone_id"],
-            Milestone.project_id == data["project_id"],
-        ).first()
     if not milestone:
         raise HTTPException(status_code=404, detail="Milestone not found")
 
@@ -237,7 +225,7 @@ def create_task(task_in: schemas.TaskCreate, bg: BackgroundTasks, db: Session =
     bg.add_task(
         fire_webhooks_sync,
         event,
-        {"task_id": db_task.id, "title": db_task.title, "type": db_task.task_type, "status": db_task.status.value},
+        {"task_code": db_task.task_code, "title": db_task.title, "type": db_task.task_type, "status": db_task.status.value},
         db_task.project_id,
         db,
     )
@@ -247,22 +235,22 @@ def create_task(task_in: schemas.TaskCreate, bg: BackgroundTasks, db: Session =
 
 @router.get("/tasks")
 def list_tasks(
-    project_id: int = None, task_status: str = None, task_type: str = None, task_subtype: str = None,
+    task_status: str = None, task_type: str = None, task_subtype: str = None,
     assignee_id: int = None, tag: str = None,
     sort_by: str = "created_at", sort_order: str = "desc",
     page: int = 1, page_size: int = 50,
-    project: str = None, milestone: str = None, status_value: str = Query(None, alias="status"), taken_by: str = None,
+    project_code: str = None, milestone_code: str = None, status_value: str = Query(None, alias="status"), taken_by: str = None,
     order_by: str = None,
     db: Session = Depends(get_db)
 ):
     query = db.query(Task)
 
-    resolved_project_id = _resolve_project_id(db, project_id, project)
+    resolved_project_id = _resolve_project_id(db, project_code)
     if resolved_project_id:
         query = query.filter(Task.project_id == resolved_project_id)
 
-    if milestone:
-        milestone_obj = _resolve_milestone(db, None, milestone, resolved_project_id)
+    if milestone_code:
+        milestone_obj = _resolve_milestone(db, milestone_code, resolved_project_id)
         query = query.filter(Task.milestone_id == milestone_obj.id)
 
     effective_status = status_value or task_status
@@ -316,14 +304,14 @@ def list_tasks(
 @router.get("/tasks/search", response_model=List[schemas.TaskResponse])
 def search_tasks_alias(
     q: str,
-    project: str = None,
+    project_code: str = None,
     status: str = None,
     db: Session = Depends(get_db),
 ):
     query = db.query(Task).filter(
         (Task.title.contains(q)) | (Task.description.contains(q))
     )
-    resolved_project_id = _resolve_project_id(db, None, project)
+    resolved_project_id = _resolve_project_id(db, project_code)
     if resolved_project_id:
         query = query.filter(Task.project_id == resolved_project_id)
     if status:
@@ -332,15 +320,15 @@ def search_tasks_alias(
     return [_serialize_task(db, i) for i in items]
 
 
-@router.get("/tasks/{task_id}", response_model=schemas.TaskResponse)
-def get_task(task_id: str, db: Session = Depends(get_db)):
-    task = _resolve_task(db, task_id)
+@router.get("/tasks/{task_code}", response_model=schemas.TaskResponse)
+def get_task(task_code: str, db: Session = Depends(get_db)):
+    task = _resolve_task(db, task_code)
     return _serialize_task(db, task)
 
 
-@router.patch("/tasks/{task_id}", response_model=schemas.TaskResponse)
-def update_task(task_id: str, task_update: schemas.TaskUpdate, db: Session = Depends(get_db), current_user: models.User = Depends(get_current_user_or_apikey)):
-    task = _resolve_task(db, task_id)
+@router.patch("/tasks/{task_code}", response_model=schemas.TaskResponse)
+def update_task(task_code: str, task_update: schemas.TaskUpdate, db: Session = Depends(get_db), current_user: models.User = Depends(get_current_user_or_apikey)):
+    task = _resolve_task(db, task_code)
 
     # P5.7: status-based edit restrictions
     current_status = task.status.value if hasattr(task.status, 'value') else task.status
@@ -437,9 +425,9 @@ def update_task(task_id: str, task_update: schemas.TaskUpdate, db: Session = Dep
     return _serialize_task(db, task)
 
 
-@router.delete("/tasks/{task_id}", status_code=status.HTTP_204_NO_CONTENT)
-def delete_task(task_id: str, db: Session = Depends(get_db), current_user: models.User = Depends(get_current_user_or_apikey)):
-    task = _resolve_task(db, task_id)
+@router.delete("/tasks/{task_code}", status_code=status.HTTP_204_NO_CONTENT)
+def delete_task(task_code: str, db: Session = Depends(get_db), current_user: models.User = Depends(get_current_user_or_apikey)):
+    task = _resolve_task(db, task_code)
     check_project_role(db, current_user.id, task.project_id, min_role="mgr")
     log_activity(db, "task.deleted", "task", task.id, current_user.id, {"title": task.title})
     db.delete(task)
@@ -454,9 +442,9 @@ class TransitionBody(BaseModel):
     comment: Optional[str] = None
 
 
-@router.post("/tasks/{task_id}/transition", response_model=schemas.TaskResponse)
+@router.post("/tasks/{task_code}/transition", response_model=schemas.TaskResponse)
 def transition_task(
-    task_id: str,
+    task_code: str,
     bg: BackgroundTasks,
     new_status: str | None = None,
     body: TransitionBody = None,
@@ -467,7 +455,7 @@ def transition_task(
     valid_statuses = [s.value for s in TaskStatus]
     if new_status not in valid_statuses:
         raise HTTPException(status_code=400, detail=f"Invalid status. Must be one of: {valid_statuses}")
-    task = _resolve_task(db, task_id)
+    task = _resolve_task(db, task_code)
     old_status = task.status.value if hasattr(task.status, 'value') else task.status
 
     # P5.1: enforce state-machine
@@ -547,18 +535,18 @@ def transition_task(
 
     event = "task.closed" if new_status == "closed" else "task.updated"
     bg.add_task(fire_webhooks_sync, event,
-                {"task_id": task.id, "title": task.title, "old_status": old_status, "new_status": new_status},
+                {"task_code": task.task_code, "title": task.title, "old_status": old_status, "new_status": new_status},
                 task.project_id, db)
     return _serialize_task(db, task)
 
 
-@router.post("/tasks/{task_id}/take", response_model=schemas.TaskResponse)
+@router.post("/tasks/{task_code}/take", response_model=schemas.TaskResponse)
 def take_task(
-    task_id: str,
+    task_code: str,
     db: Session = Depends(get_db),
     current_user: models.User = Depends(get_current_user_or_apikey),
 ):
-    task = _find_task_by_id_or_code(db, task_id)
+    task = _find_task_by_code(db, task_code)
     if not task:
         raise HTTPException(status_code=404, detail="Task not found")
 
@@ -577,7 +565,7 @@ def take_task(
         db,
         current_user.id,
         "task.assigned",
-        f"Task {task.task_code or task.id} assigned to you",
+        f"Task {task.task_code} assigned to you",
         f"'{task.title}' has been assigned to you.",
         "task",
         task.id,
@@ -587,9 +575,9 @@ def take_task(
 
 # ---- Assignment ----
 
-@router.post("/tasks/{task_id}/assign")
-def assign_task(task_id: str, assignee_id: int, db: Session = Depends(get_db)):
-    task = _resolve_task(db, task_id)
+@router.post("/tasks/{task_code}/assign")
+def assign_task(task_code: str, assignee_id: int, db: Session = Depends(get_db)):
+    task = _resolve_task(db, task_code)
     user = db.query(models.User).filter(models.User.id == assignee_id).first()
     if not user:
         raise HTTPException(status_code=404, detail="User not found")
@@ -597,33 +585,33 @@ def assign_task(task_id: str, assignee_id: int, db: Session = Depends(get_db)):
     db.commit()
     db.refresh(task)
     _notify_user(db, assignee_id, "task.assigned",
-                 f"Task #{task.id} assigned to you",
+                 f"Task {task.task_code} assigned to you",
                  f"'{task.title}' has been assigned to you.", "task", task.id)
-    return {"task_id": task.id, "assignee_id": assignee_id, "title": task.title}
+    return {"task_code": task.task_code, "assignee_id": assignee_id, "title": task.title}
 
 
 # ---- Tags ----
 
-@router.post("/tasks/{task_id}/tags")
-def add_tag(task_id: str, tag: str, db: Session = Depends(get_db)):
-    task = _resolve_task(db, task_id)
+@router.post("/tasks/{task_code}/tags")
+def add_tag(task_code: str, tag: str, db: Session = Depends(get_db)):
+    task = _resolve_task(db, task_code)
     current = set(task.tags.split(",")) if task.tags else set()
     current.add(tag.strip())
     current.discard("")
     task.tags = ",".join(sorted(current))
     db.commit()
-    return {"task_id": task_id, "tags": list(current)}
+    return {"task_code": task.task_code, "tags": list(current)}
 
 
-@router.delete("/tasks/{task_id}/tags")
-def remove_tag(task_id: str, tag: str, db: Session = Depends(get_db)):
-    task = _resolve_task(db, task_id)
+@router.delete("/tasks/{task_code}/tags")
+def remove_tag(task_code: str, tag: str, db: Session = Depends(get_db)):
+    task = _resolve_task(db, task_code)
     current = set(task.tags.split(",")) if task.tags else set()
     current.discard(tag.strip())
     current.discard("")
     task.tags = ",".join(sorted(current)) if current else None
     db.commit()
-    return {"task_id": task_id, "tags": list(current)}
+    return {"task_code": task.task_code, "tags": list(current)}
 
 
 @router.get("/tags")
@@ -643,12 +631,12 @@ def list_all_tags(project_id: int = None, db: Session = Depends(get_db)):
 # ---- Batch ----
 
 class BatchAssign(BaseModel):
-    task_ids: List[int]
+    task_codes: List[str]
     assignee_id: int
 
 
 class BatchTransitionBody(BaseModel):
-    task_ids: List[int]
+    task_codes: List[str]
     new_status: str
     comment: Optional[str] = None
 
@@ -665,17 +653,17 @@ def batch_transition(
         raise HTTPException(status_code=400, detail="Invalid status")
     updated = []
     skipped = []
-    for task_id in data.task_ids:
-        task = db.query(Task).filter(Task.id == task_id).first()
+    for task_code in data.task_codes:
+        task = db.query(Task).filter(Task.task_code == task_code).first()
         if not task:
-            skipped.append({"id": task_id, "title": None, "old": None,
+            skipped.append({"task_code": task_code, "title": None, "old": None,
                             "reason": "Task not found"})
             continue
         old_status = task.status.value if hasattr(task.status, 'value') else task.status
         # P5.1: state-machine check
         allowed = VALID_TRANSITIONS.get(old_status, set())
         if data.new_status not in allowed:
-            skipped.append({"id": task.id, "title": task.title, "old": old_status,
+            skipped.append({"task_code": task.task_code, "title": task.title, "old": old_status,
                             "reason": f"Cannot transition from '{old_status}' to '{data.new_status}'"})
             continue
 
@@ -685,23 +673,23 @@ def batch_transition(
             if milestone:
                 ms_status = milestone.status.value if hasattr(milestone.status, 'value') else milestone.status
                 if ms_status != "undergoing":
-                    skipped.append({"id": task.id, "title": task.title, "old": old_status,
+                    skipped.append({"task_code": task.task_code, "title": task.title, "old": old_status,
                                     "reason": f"Milestone is '{ms_status}', must be 'undergoing'"})
                     continue
             dep_result = check_task_deps(db, task.depend_on)
             if not dep_result.ok:
-                skipped.append({"id": task.id, "title": task.title, "old": old_status,
+                skipped.append({"task_code": task.task_code, "title": task.title, "old": old_status,
                                 "reason": dep_result.reason})
                 continue
 
         # P5.3: open → undergoing requires assignee == current_user
         if old_status == "open" and data.new_status == "undergoing":
             if not task.assignee_id:
-                skipped.append({"id": task.id, "title": task.title, "old": old_status,
+                skipped.append({"task_code": task.task_code, "title": task.title, "old": old_status,
                                 "reason": "Assignee must be set before starting"})
                 continue
             if current_user.id != task.assignee_id:
-                skipped.append({"id": task.id, "title": task.title, "old": old_status,
+                skipped.append({"task_code": task.task_code, "title": task.title, "old": old_status,
                                 "reason": "Only the assigned user can start this task"})
                 continue
 
@@ -709,11 +697,11 @@ def batch_transition(
         if old_status == "undergoing" and data.new_status == "completed":
             comment_text = data.comment
             if not comment_text or not comment_text.strip():
-                skipped.append({"id": task.id, "title": task.title, "old": old_status,
+                skipped.append({"task_code": task.task_code, "title": task.title, "old": old_status,
                                 "reason": "A completion comment is required"})
                 continue
             if task.assignee_id and current_user.id != task.assignee_id:
-                skipped.append({"id": task.id, "title": task.title, "old": old_status,
+                skipped.append({"task_code": task.task_code, "title": task.title, "old": old_status,
                                 "reason": "Only the assigned user can complete this task"})
                 continue
 
@@ -722,7 +710,7 @@ def batch_transition(
             try:
                 check_permission(db, current_user.id, task.project_id, "task.close")
             except HTTPException:
-                skipped.append({"id": task.id, "title": task.title, "old": old_status,
+                skipped.append({"task_code": task.task_code, "title": task.title, "old": old_status,
                                 "reason": "Missing 'task.close' permission"})
                 continue
 
@@ -732,7 +720,7 @@ def batch_transition(
             try:
                 check_permission(db, current_user.id, task.project_id, perm)
             except HTTPException:
-                skipped.append({"id": task.id, "title": task.title, "old": old_status,
+                skipped.append({"task_code": task.task_code, "title": task.title, "old": old_status,
                                 "reason": f"Missing '{perm}' permission"})
                 continue
             task.finished_on = None
@@ -742,7 +730,7 @@ def batch_transition(
         if data.new_status in ("closed", "completed") and not task.finished_on:
             task.finished_on = datetime.utcnow()
         task.status = data.new_status
-        updated.append({"id": task.id, "title": task.title, "old": old_status, "new": data.new_status})
+        updated.append({"task_code": task.task_code, "title": task.title, "old": old_status, "new": data.new_status})
 
         # Activity log per task
         log_activity(db, f"task.transition.{data.new_status}", "task", task.id, current_user.id,
@@ -762,7 +750,7 @@ def batch_transition(
     # P3.5: auto-complete milestone for any completed task
     for u in updated:
         if u["new"] == "completed":
-            t = db.query(Task).filter(Task.id == u["id"]).first()
+            t = db.query(Task).filter(Task.task_code == u["task_code"]).first()
             if t:
                 from app.api.routers.milestone_actions import try_auto_complete_milestone
                 try_auto_complete_milestone(db, t, user_id=current_user.id)
@@ -782,25 +770,27 @@ def batch_assign(data: BatchAssign, db: Session = Depends(get_db)):
     if not user:
         raise HTTPException(status_code=404, detail="Assignee not found")
     updated = []
-    for task_id in data.task_ids:
-        task = db.query(Task).filter(Task.id == task_id).first()
+    for task_code in data.task_codes:
+        task = db.query(Task).filter(Task.task_code == task_code).first()
         if task:
             task.assignee_id = data.assignee_id
-            updated.append(task_id)
+            updated.append(task.task_code)
     db.commit()
-    return {"updated": len(updated), "task_ids": updated, "assignee_id": data.assignee_id}
+    return {"updated": len(updated), "task_codes": updated, "assignee_id": data.assignee_id}
 
 
 # ---- Search ----
 
 @router.get("/search/tasks")
-def search_tasks(q: str, project_id: int = None, page: int = 1, page_size: int = 50,
+def search_tasks(q: str, project_code: str = None, page: int = 1, page_size: int = 50,
                  db: Session = Depends(get_db)):
     query = db.query(Task).filter(
         (Task.title.contains(q)) | (Task.description.contains(q))
     )
-    if project_id:
-        query = query.filter(Task.project_id == project_id)
+    if project_code:
+        project_id = _resolve_project_id(db, project_code)
+        if project_id:
+            query = query.filter(Task.project_id == project_id)
     total = query.count()
     page = max(1, page)
     page_size = min(max(1, page_size), 200)
diff --git a/app/main.py b/app/main.py
index 3dd9b9d..45ef1a9 100644
--- a/app/main.py
+++ b/app/main.py
@@ -140,6 +140,8 @@ def _migrate_schema():
         if not result.fetchone():
             db.execute(text("ALTER TABLE projects ADD COLUMN project_code VARCHAR(16) NULL"))
             db.execute(text("CREATE UNIQUE INDEX idx_projects_project_code ON projects (project_code)"))
+        else:
+            db.execute(text("CREATE UNIQUE INDEX IF NOT EXISTS idx_projects_project_code ON projects (project_code)"))
 
         # projects.owner_name
         result = db.execute(text("SHOW COLUMNS FROM projects LIKE 'owner_name'"))
@@ -173,6 +175,8 @@ def _migrate_schema():
         if not result.fetchone():
             db.execute(text("ALTER TABLE tasks ADD COLUMN created_by_id INTEGER NULL"))
             _ensure_fk(db, "tasks", "created_by_id", "users", "id", "fk_tasks_created_by_id")
+        if _has_column(db, "tasks", "task_code"):
+            db.execute(text("CREATE UNIQUE INDEX IF NOT EXISTS idx_tasks_task_code ON tasks (task_code)"))
 
         # milestones creator field
         result = db.execute(text("SHOW COLUMNS FROM milestones LIKE 'created_by_id'"))
@@ -202,6 +206,8 @@ def _migrate_schema():
 
         # --- Milestone status enum migration (old -> new) ---
         if _has_table(db, "milestones"):
+            if _has_column(db, "milestones", "milestone_code"):
+                db.execute(text("CREATE UNIQUE INDEX IF NOT EXISTS idx_milestones_milestone_code ON milestones (milestone_code)"))
             # Alter enum column to accept new values
             db.execute(text(
                 "ALTER TABLE milestones MODIFY COLUMN status "
@@ -257,6 +263,18 @@ def _migrate_schema():
         if _has_table(db, "server_states") and not _has_column(db, "server_states", "plugin_version"):
             db.execute(text("ALTER TABLE server_states ADD COLUMN plugin_version VARCHAR(64) NULL"))
 
+        if _has_table(db, "meetings") and _has_column(db, "meetings", "meeting_code"):
+            db.execute(text("CREATE UNIQUE INDEX IF NOT EXISTS idx_meetings_meeting_code ON meetings (meeting_code)"))
+
+        if _has_table(db, "supports") and _has_column(db, "supports", "support_code"):
+            db.execute(text("CREATE UNIQUE INDEX IF NOT EXISTS idx_supports_support_code ON supports (support_code)"))
+
+        if _has_table(db, "proposes") and _has_column(db, "proposes", "propose_code"):
+            db.execute(text("CREATE UNIQUE INDEX IF NOT EXISTS idx_proposes_propose_code ON proposes (propose_code)"))
+
+        if _has_table(db, "essentials") and _has_column(db, "essentials", "essential_code"):
+            db.execute(text("CREATE UNIQUE INDEX IF NOT EXISTS idx_essentials_essential_code ON essentials (essential_code)"))
+
         # --- server_states nginx telemetry for generic monitor client ---
         if _has_table(db, "server_states") and not _has_column(db, "server_states", "nginx_installed"):
             db.execute(text("ALTER TABLE server_states ADD COLUMN nginx_installed BOOLEAN NULL"))
diff --git a/app/schemas/schemas.py b/app/schemas/schemas.py
index 6bd1443..ef8e8e1 100644
--- a/app/schemas/schemas.py
+++ b/app/schemas/schemas.py
@@ -43,9 +43,7 @@ class TaskBase(BaseModel):
 
 
 class TaskCreate(TaskBase):
-    project_id: Optional[int] = None
     project_code: Optional[str] = None
-    milestone_id: Optional[int] = None
     milestone_code: Optional[str] = None
     reporter_id: Optional[int] = None
     assignee_id: Optional[int] = None
@@ -75,15 +73,12 @@ class TaskUpdate(BaseModel):
 
 
 class TaskResponse(TaskBase):
-    id: int
     status: TaskStatusEnum
     task_code: Optional[str] = None
     code: Optional[str] = None
     type: Optional[str] = None
     due_date: Optional[datetime] = None
-    project_id: int
     project_code: Optional[str] = None
-    milestone_id: int
     milestone_code: Optional[str] = None
     reporter_id: int
     assignee_id: Optional[int] = None
@@ -94,8 +89,8 @@ class TaskResponse(TaskBase):
     positions: Optional[str] = None
     pending_matters: Optional[str] = None
     # BE-PR-008: Proposal Accept tracking
-    source_proposal_id: Optional[int] = None
-    source_essential_id: Optional[int] = None
+    source_proposal_code: Optional[str] = None
+    source_essential_code: Optional[str] = None
     created_at: datetime
     updated_at: Optional[datetime] = None
     
@@ -259,9 +254,9 @@ class MilestoneUpdate(BaseModel):
 
 
 class MilestoneResponse(MilestoneBase):
-    id: int
     milestone_code: Optional[str] = None
-    project_id: int
+    code: Optional[str] = None
+    project_code: Optional[str] = None
     created_by_id: Optional[int] = None
     started_at: Optional[datetime] = None
     created_at: datetime
@@ -285,7 +280,7 @@ class ProposalBase(BaseModel):
 
 
 class ProposalCreate(ProposalBase):
-    project_id: Optional[int] = None
+    pass
 
 
 class ProposalUpdate(BaseModel):
@@ -294,11 +289,10 @@ class ProposalUpdate(BaseModel):
 
 
 class ProposalResponse(ProposalBase):
-    id: int
     proposal_code: Optional[str] = None  # preferred name
     propose_code: Optional[str] = None   # backward compat alias (same value)
     status: ProposalStatusEnum
-    project_id: int
+    project_code: Optional[str] = None
     created_by_id: Optional[int] = None
     created_by_username: Optional[str] = None
     feat_task_id: Optional[str] = None   # DEPRECATED (BE-PR-010): legacy field, read-only. Use generated_tasks instead.
@@ -340,9 +334,8 @@ class EssentialUpdate(BaseModel):
 
 
 class EssentialResponse(EssentialBase):
-    id: int
     essential_code: str
-    proposal_id: int
+    proposal_code: Optional[str] = None
     created_by_id: Optional[int] = None
     created_at: datetime
     updated_at: Optional[datetime] = None
@@ -353,13 +346,12 @@ class EssentialResponse(EssentialBase):
 
 class GeneratedTaskBrief(BaseModel):
     """Brief info about a story task generated from Proposal Accept."""
-    task_id: int
     task_code: Optional[str] = None
     task_type: str
     task_subtype: Optional[str] = None
     title: str
     status: Optional[str] = None
-    source_essential_id: Optional[int] = None
+    source_essential_code: Optional[str] = None
 
 
 class ProposalDetailResponse(ProposalResponse):
@@ -374,12 +366,10 @@ class ProposalDetailResponse(ProposalResponse):
 
 class GeneratedTaskSummary(BaseModel):
     """Brief summary of a task generated from a Proposal Essential."""
-    task_id: int
     task_code: str
     task_type: str
     task_subtype: str
     title: str
-    essential_id: int
     essential_code: str