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/database.ts

@@ -94,9 +94,10 @@ export class AppDatabase extends AppDatabaseBase {
   createDocumentRevision(input: { documentId: string; companyId: string; body: string; changeSummary?: string | null; createdByAgentId?: string | null; createdByUserId?: string | null }) { return this.documentsMod.createDocumentRevision(input); }
   getDocumentLatestRevisionId(documentId: string) { return this.documentsMod.getDocumentLatestRevisionId(documentId); }
   listDocumentRevisions(documentId: string, companyId: string) { return this.documentsMod.listDocumentRevisions(documentId, companyId); }
-  createWorkProduct(input: { companyId: string; taskId: string; projectId?: string | null; type: string; provider: string; externalId?: string | null; title: string; url?: string | null; status?: string; reviewState?: string; isPrimary?: boolean; summary?: string | null; metadataJson?: string | null; createdByRunId?: string | null }) { return this.documentsMod.createWorkProduct(input); }
+  createWorkProduct(input: { companyId: string; taskId: string | null; projectId?: string | null; type: string; provider: string; externalId?: string | null; title: string; url?: string | null; status?: string; reviewState?: string; isPrimary?: boolean; summary?: string | null; metadataJson?: string | null; createdByRunId?: string | null }) { return this.documentsMod.createWorkProduct(input); }
   updateWorkProduct(id: string, companyId: string, patch: Parameters<ReturnType<typeof import("./database/documents").buildDocumentMethods>["updateWorkProduct"]>[2]) { return this.documentsMod.updateWorkProduct(id, companyId, patch); }
   listWorkProductsForTask(taskId: string, companyId: string) { return this.documentsMod.listWorkProductsForTask(taskId, companyId); }
+  findWorkProductByExternalId(companyId: string, provider: string, externalId: string) { return this.documentsMod.findWorkProductByExternalId(companyId, provider, externalId); }
   deleteWorkProduct(id: string, companyId: string) { return this.documentsMod.deleteWorkProduct(id, companyId); }
   linkDocumentToTask(taskId: string, documentId: string, companyId: string, key: string) { return this.documentsMod.linkDocumentToTask(taskId, documentId, companyId, key); }
   unlinkDocumentFromTask(taskId: string, key: string, companyId: string) { this.documentsMod.unlinkDocumentFromTask(taskId, key, companyId); }