refactor(cost): single writer for cost_entries, finishRun reads SUM

Cost was written through three independent paths: worker-runner shipped
`finalUsage.costUsd` in run-finished -> finishRun wrote `runs.cost_usd`,
`tasks.cost_usd += costUsd`, `agents.spent_monthly_usd += costUsd`, and
inserted a per-run aggregate row in cost_entries. CostWriter
additionally inserted per-message rows in cost_entries from main. Any
CostWriter failure created silent drift between `SUM(cost_entries)`
(read by budget enforcement) and `runs.cost_usd` (read by the UI).

Make CostWriter the single writer, finishRun the single reader.

- Add `db.recordCostEntry(...)` as the first-class insert path for
  per-message cost rows. CostWriter calls it; tests call it directly.
- Remove the aggregate INSERT from finishRun. finishRun now reads
  `SELECT COALESCE(SUM(amount_usd), 0) FROM cost_entries WHERE run_id=?
  AND unattributed=0` and writes that as the authoritative run total to
  runs.cost_usd, tasks.cost_usd, and agents.spent_monthly_usd.
- Drop `costUsd` from `finishRun` input, the worker `run-finished`
  ChildMessage shape, the automation `RunFinishedEvent` type, and every
  caller + test fixture. Cost is owned by the per-message path.
- worker-runner stops extracting `usage.cost.total` — token counts stay
  for session accumulation, cost comes from pi-ai via CostWriter.
- run-finished-helpers now gates budget incident checks on
  `event.status === "succeeded"` instead of a cost field that no longer
  exists on the event.
- automation-run-completion fires `budget_threshold` on every succeeded
  run (post-run spent_monthly_usd already reflects the SUM path).
- Update budget tests to write a `recordCostEntry` before `finishRun`
  to simulate the per-message cost path; drop `costUsd` from cross-
  subsystem, edge-case-budget, database, and related fixtures.

One writer, one reader, one source of truth. No drift.

src/main/worker/handlers/run-finished-helpers.ts

@@ -48,7 +48,6 @@ export function finalizeRun(
       signal: event.signal,
       model: event.model,
       sessionDisplayId: event.sessionDisplayId,
-      costUsd: event.costUsd,
       unattributedCost: event.unattributedCost,
       inputTokens: event.inputTokens,
       outputTokens: event.outputTokens,
@@ -186,10 +185,10 @@ export function runPostCompletionAutomation(
   const { destroyed, MAX_RETRY_ATTEMPTS, RETRY_COOLDOWN_MS, pendingRetryTimers } = context;
   const { run, task } = rfCtx;
 
-  // Policy-based incident check after run completion (Phase 5). Reuse the
-  // `task` already resolved in finalizeRun instead of double-fetching with
-  // its own catch-and-swallow; if task is null the project-scope is null.
-  if (budgetService && typeof event.costUsd === "number" && Number.isFinite(event.costUsd)) {
+  // Policy-based incident check after run completion. Always runs once the
+  // run is finalized — cost is read from the cost_entries SUM inside
+  // finishRun/checkAndCreateIncidents, not from the worker event.
+  if (budgetService && event.status === "succeeded") {
     budgetService.checkAndCreateIncidents(run.companyId, run.agentId, task?.projectId ?? null);
   }
 

src/main/worker/worker-crash-recovery.ts

@@ -42,7 +42,6 @@ export function handleWorkerExit(
         signal: null,
         model: null,
         sessionDisplayId: null,
-        costUsd: null,
         unattributedCost: true,
       });
       if (run.workspaceId) {
@@ -128,7 +127,6 @@ export function handleWorkerExit(
           signal: null,
           model: null,
           sessionDisplayId: null,
-          costUsd: null,
           unattributedCost: true,
         });
         if (candidate.workspaceId) {

src/main/worker/worker-entry.ts

@@ -88,7 +88,6 @@ function cancelRun(runId: string) {
       model: null,
       sessionParams: null,
       sessionDisplayId: null,
-      costUsd: null,
       unattributedCost: true,
       inputTokens: null,
       outputTokens: null,

src/main/worker/worker-helpers.ts

@@ -43,7 +43,6 @@ export type ChildMessage =
       model: string | null;
       sessionParams: Record<string, unknown> | null;
       sessionDisplayId: string | null;
-      costUsd: number | null;
       unattributedCost: boolean;
       inputTokens: number | null;
       outputTokens: number | null;

src/main/worker/worker-runner.ts

@@ -65,10 +65,9 @@ export class WorkerRunner {
     post({ type: "run-status", runId: job.runId, status: "running", message: `Running agent ${job.agentName}.` });
 
     let resolvedModelId: string | null = job.model;
-    let finalUsage: { inputTokens: number | null; outputTokens: number | null; costUsd: number | null } = {
+    let finalUsage: { inputTokens: number | null; outputTokens: number | null } = {
       inputTokens: null,
       outputTokens: null,
-      costUsd: null,
     };
     let errorMessage: string | null = null;
 
@@ -177,7 +176,6 @@ export class WorkerRunner {
               finalUsage = {
                 inputTokens: typeof maybeAssistant.usage.input === "number" ? maybeAssistant.usage.input : finalUsage.inputTokens,
                 outputTokens: typeof maybeAssistant.usage.output === "number" ? maybeAssistant.usage.output : finalUsage.outputTokens,
-                costUsd: typeof maybeAssistant.usage.cost?.total === "number" ? maybeAssistant.usage.cost.total : finalUsage.costUsd,
               };
             }
           }
@@ -227,8 +225,12 @@ export class WorkerRunner {
       model: resolvedModelId,
       sessionParams: job.sessionParams,
       sessionDisplayId: null,
-      costUsd: finalUsage.costUsd,
-      unattributedCost: finalUsage.costUsd === null,
+      // Worker no longer owns cost attribution — CostWriter (main-side)
+      // writes per-message rows, finishRun sums them. This flag stays true
+      // only for run paths that never had a chance to emit usage (errors
+      // before the first message_end); per-message drift detection belongs
+      // elsewhere.
+      unattributedCost: finalUsage.inputTokens === null,
       inputTokens: finalUsage.inputTokens,
       outputTokens: finalUsage.outputTokens,
     });

src/main/worker/worker-types.ts

@@ -32,7 +32,6 @@ export const workerMessageSchema = z.union([
     model: z.string().nullable(),
     sessionParams: z.record(z.string(), z.unknown()).nullable(),
     sessionDisplayId: z.string().nullable(),
-    costUsd: z.number().nullable(),
     unattributedCost: z.boolean(),
     inputTokens: z.number().nullable(),
     outputTokens: z.number().nullable(),