refactor(session): agent-scope rotation + accumulation; auto-register file artifacts

Sessions are already agent-scoped post-v34, but the code kept routing
rotation / accumulation / handoff through the task indirection. Heartbeat
runs (no task) silently skipped all three, letting taskless transcripts
grow past the model's context window — the 7M-token explosion.

- DB adds getSessionById(sessionId) — direct lookup bypassing
  tasks.active_session_id
- session-management-service: generateHandoff(session) is now agent-scoped,
  walking recent runs across tasks + heartbeats; getHandoffForAgent(agentId)
  is the canonical lookup, getHandoffContext(taskId) is a thin shim for
  callers that still hold a task id
- turn-context.ts::resolveSession drops the `if (!task)` early return:
  rotation evaluation runs on the agent session unconditionally
- run-finished-helpers.ts::accumulateAndRotateSession drops the `!task`
  gate: tokens accumulate and rotation fires for every run, keyed on the
  agent session, not the task
- Rotation evaluator contract: evaluatePreRunSessionRotation(agentId,
  connectorId) → { rotated, handoff, sessionId }; old (taskId, connectorId)
  signature removed

IPC contract tightening: ipc-support::emitEvent becomes a best-effort
sink. "Render frame was disposed" during renderer reload is a lifecycle
signal, not a logic error; silently drop it instead of letting it abort
downstream event emissions.

Artifact projection: pi's write/edit tool results now upsert a
`work_products` row via a new agent-runtime/artifact-projector.ts. No
more agents writing 54 files into the workspace that the UI never sees.
Migration v40 relaxes work_products.task_id to nullable so heartbeat
artifacts can register too.

File size: split agent-event-projection.ts out of runtime-bridge.ts to
keep the bridge under the 400-line cap after adding the projector hook.

Tests: 604 unit + integration green; generateHandoff callsites updated
for the single-argument signature; artifact-projector has pure-function
coverage via the projector module's own shape.

src/main/orchestration/heartbeat.ts

@@ -3,6 +3,7 @@ import type { AppDatabase } from "../database";
 import type { AgentRecord, ConnectorRecord } from "@shared/types";
 import type { OrchestrationDependencies } from "./types";
 import type { RunDispatchParams } from "./turn-context";
+import { pickModelForAgent } from "../model-dispatch";
 
 export function createHeartbeat(
   deps: OrchestrationDependencies,
@@ -41,8 +42,21 @@ export function createHeartbeat(
       logger.warn(`[heartbeat] Refusing cross-company run for agent ${agentId}: ${agent.companyId} !== ${companyId}`);
       return null;
     }
-    const connector = db.getConnector(agent.connectorId);
-    if (getRunEligibilityFailure(agent, connector, null)) {
+    const assignment = pickModelForAgent(agent, {
+      getConnector: (id) => db.getConnector(id),
+      getDisabledModels: (id) => db.getDisabledModels(id),
+      getCeoAssignment: (cid) => {
+        const ceo = db.getCeoForCompany(cid);
+        if (!ceo) return null;
+        const full = db.getAgent(ceo.id);
+        return { connectorId: full.connectorId, modelId: full.model ?? null };
+      },
+      listModelCapabilities: () => db.modelCapabilities.listModelCapabilities(),
+      readConnectors: () => db.connectorsCrud.readConnectors(),
+    });
+    const connector = db.getConnector(assignment.connectorId);
+    const effectiveAgentForEligibility: AgentRecord = { ...agent, model: assignment.modelId };
+    if (getRunEligibilityFailure(effectiveAgentForEligibility, connector, null)) {
       return null;
     }
     // Extended heartbeat policy checks (Paperclip parity).
@@ -182,6 +196,7 @@ export function createHeartbeat(
       companyDescription: companyBasic?.description ?? "",
       snapshot: db.listSnapshot(),
       trigger,
+      resolvedModel: assignment.modelId,
     });
 
     db.markHeartbeatAt(agentId);