feat(gemini): plexum-host MCP exposure + real consume mirror

Same architecture as the codex sister change:

1. mcp-host subcommand routes argv[1] to mcpbridge.Run, reading
   PLEXUM_MCP_SOCKET / PLEXUM_MCP_AGENT_ID from gemini-cli's
   `gemini mcp add --env` env baking.

2. EnsureGeminiMCPRegistered handles per-agent stable registration
   under `-s user --trust` so gemini auto-approves the tool surface.

3. Post-turn ParseGeminiToolCalls + EmitGeminiToolCalls scans the
   chat JSONL at ~/.gemini/tmp/<ws>/chats/session-*.jsonl. Pairs
   gemini's nested `toolCalls[].id` with the matching
   `functionResponse.id` from later user lines.

4. MutateGeminiSession rewrites the chat JSONL: toolCalls[].args
   → {} (heavy), functionResponse.response.output → marker.

E2E verified: gemini call exec via plexum-host → dynamic.jsonl
records the call → dynamic-tool-clear consumes → gemini session
mirrored → resume gemini sees consumed marker not the original.

internal/runner/runner.go

@@ -26,6 +26,7 @@ import (
 	"path/filepath"
 
 	"git.hangman-lab.top/hzhang/Plexum-sdk-go/canonical"
+	"git.hangman-lab.top/hzhang/Plexum-sdk-go/mcpbridge"
 	plugin "git.hangman-lab.top/hzhang/Plexum-sdk-go/plugin"
 )
 
@@ -58,6 +59,25 @@ func Run(
 		return nil, errors.New("gemini: no user text in request messages")
 	}
 
+	// Per-turn MCP bridge so gemini can call Plexum host tools the
+	// host advertised in req.Tools. Best-effort.
+	var br *mcpbridge.Bridge
+	if len(req.Tools) > 0 {
+		exe, err := os.Executable()
+		if err == nil {
+			if _, regErr := EnsureGeminiMCPRegistered(ctx, binary, exe, agent.AgentID); regErr != nil {
+				host.Log("warn", "gemini: mcp registration failed", map[string]any{"err": regErr.Error()})
+			} else {
+				b, err := mcpbridge.SetupOnPath(ctx, host, agent.AgentID, req.Tools, StableSocketPath(agent.AgentID))
+				if err != nil {
+					host.Log("warn", "gemini: bridge setup failed", map[string]any{"err": err.Error()})
+				} else {
+					br = b
+				}
+			}
+		}
+	}
+
 	resumeID := loadSessionID(workspace)
 
 	args := []string{"--skip-trust", "--output-format", "json"}
@@ -156,6 +176,21 @@ func Run(
 			})
 		}
 
+		// Post-turn: scan gemini's chat JSONL for tool calls and emit
+		// them as canonical events so dynamic.jsonl captures the real
+		// ids (same ones SessionMutator will rewrite on consume).
+		if sessionPath, perr := FindGeminiSessionFile(workspace); perr == nil {
+			calls, perr := ParseGeminiToolCalls(sessionPath)
+			if perr != nil {
+				host.Log("warn", "gemini: parse session failed",
+					map[string]any{"err": perr.Error(), "path": sessionPath})
+			} else {
+				EmitGeminiToolCalls(calls, emit)
+				host.Log("debug", "gemini: emitted tool calls from session",
+					map[string]any{"count": len(calls), "path": sessionPath})
+			}
+		}
+
 		var usage canonical.Usage
 		for _, m := range resp.Stats.Models {
 			usage.InputTokens += m.Tokens.Input
@@ -172,6 +207,7 @@ func Run(
 			StopReason: stopReason,
 			Usage: &usage,
 		})
+		br.Close() // nil-safe
 	}()
 	return out, nil
 }