feat(fabric): coalesce a split agent turn into ONE message (deterministic)

OpenClaw delivers an agent turn whose blocks are text -> thinking/tool
-> text via multiple inbound deliver() calls (a non-text block is a
delivery boundary), so one turn became N Fabric messages.

Fix: buffer deliver() segments per channel (src/coalesce.ts) and flush
them as ONE postMessage at a deterministic boundary — the finally after
dispatchInboundReplyWithBase() resolves, which provably runs only after
every deliver() of the turn (verified: deliver,deliver -> dispatch
returned -> flush). No hooks, no timers, no idle guessing. The
agent_end hook was rejected: it fires BEFORE deliver(). gateway_stop
flushes any leftover; a long safety timeout is a leak-guard only.
channels.fabric.coalesce=false restores raw per-segment posting.

Verified on local openclaw + Fabric with a fake text/thinking/text
model: single trigger -> exactly one merged message.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

dist/fabric/src/coalesce.js

@@ -0,0 +1,75 @@
+// Deterministic turn coalescer.
+//
+// OpenClaw calls the Fabric `deliver` callback once per assistant text
+// segment; a thinking/tool block between two text blocks is a delivery
+// boundary, so one agent turn of `text → thinking/tool → text` arrives as
+// multiple deliver() calls. There is no turn id on the delivery, so we
+// BUFFER segments by Fabric channelId and post the merged message when the
+// turn truly ends. The flush is driven by inbound.ts right after
+// `dispatchInboundReplyWithBase` resolves — that only happens AFTER every
+// deliver() of the turn, a deterministic boundary (NOT a timer, NOT the
+// agent_end hook, which fires before deliver()). `coalesce=false` posts
+// each segment immediately.
+const SAFETY_FLUSH_MS = 120_000; // leak-guard only; not the flush mechanism
+export function normChannelId(x) {
+    const s = String(x ?? '');
+    return s.startsWith('fabric:') ? s.slice('fabric:'.length) : s;
+}
+const pendingByChannel = new Map();
+async function flushChannel(channelId, reason) {
+    const p = pendingByChannel.get(channelId);
+    if (!p)
+        return;
+    pendingByChannel.delete(channelId);
+    clearTimeout(p.safety);
+    const text = p.parts.join('\n\n').trim();
+    if (!text)
+        return;
+    try {
+        await p.post(text);
+        p.log?.(`fabric: flushed ${p.parts.length} segment(s) channel=${channelId} (${reason})`);
+    }
+    catch (e) {
+        p.log?.(`fabric: flush FAILED channel=${channelId} (${reason}): ${String(e)}`);
+    }
+}
+// Buffer one delivered segment (or send immediately when coalesce=false).
+// `post` performs the real Fabric postMessage with the caller's already
+// resolved guild/token; on flush it is called once with the merged text.
+export async function enqueueDelivery(params) {
+    const cid = normChannelId(params.channelId);
+    const text = (params.text ?? '').trim();
+    if (!text)
+        return;
+    if (!params.coalesce) {
+        await params.post(text);
+        return;
+    }
+    const existing = pendingByChannel.get(cid);
+    if (existing) {
+        existing.parts.push(text);
+        existing.post = params.post; // freshest guild/token closure
+        existing.log = params.log;
+    }
+    else {
+        pendingByChannel.set(cid, {
+            parts: [text],
+            post: params.post,
+            log: params.log,
+            safety: setTimeout(() => void flushChannel(cid, 'safety-timeout'), SAFETY_FLUSH_MS),
+        });
+    }
+}
+// Called by the agent_end hook with the hook ctx's channelId (bare or
+// fabric:-prefixed). Deterministic per-turn boundary.
+export async function flushFabricForChannel(rawChannelId) {
+    const cid = normChannelId(rawChannelId);
+    if (cid)
+        await flushChannel(cid, 'dispatch-end');
+}
+// gateway_stop: flush anything still buffered.
+export async function flushAllFabric() {
+    for (const cid of [...pendingByChannel.keys()]) {
+        await flushChannel(cid, 'gateway_stop');
+    }
+}