feat(agent): route signal_report tasks to signals gateway product

[joshsny]

Problem

Signals/report-generation traffic currently bills to the background_agents LLM gateway product, sharing a cost pool with every other internal task (Slack-triggered runs, session-summary work, etc.). This makes it hard to track signals spend separately and apply a dedicated budget.

Changes

Route LLM gateway calls so each task type lands in the right product bucket:

• internal task with origin_product = \"signal_report\" → signals
• any other internal task → background_agents
• any other task → posthog_code

The decision was pulled out of AgentServer.configureEnvironment into a small pure helper, resolveGatewayProduct, exported from @posthog/agent next to the GatewayProduct type so the rule is independently testable and easy to reuse.

Files touched:

• `packages/agent/src/utils/gateway.ts` — add `signals` to `GatewayProduct`, add `resolveGatewayProduct` helper.
• `packages/agent/src/utils/gateway.test.ts` — unit tests for every branch of the helper.
• `packages/agent/src/server/agent-server.ts` — pass `origin_product` into `configureEnvironment` and delegate to `resolveGatewayProduct`.
• `packages/agent/src/server/agent-server.configure-environment.test.ts` — add coverage for the new signals branch and the non-internal + signal_report carve-out.
• `packages/agent/src/types.ts` — add `signal_report` to the `Task.origin_product` union.

Pairs with the gateway-side change posthog/posthog#59433 which adds the per-user cost limit for the signals product ($500/7d burst, $1000/30d sustained).

How did you test this?

I'm an agent. I ran:

• `pnpm --filter @posthog/agent test src/utils/gateway.test.ts src/server/agent-server.configure-environment.test.ts` → 12/12 passing
• biome + tsc via the pre-commit hook on the staged changes

I did not run the full test suite or any manual / end-to-end testing.

Publish to changelog?

no

[greptile-apps]

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
packages/agent/src/utils/gateway.test.ts:4-42
The five `resolveGatewayProduct` cases share identical structure — call the function with `{isInternal, originProduct}`, assert the returned `GatewayProduct` — which is the canonical candidate for `it.each`. The first test also bundles two distinct inputs (`isInternal: false` and the default call) into one assertion block, hiding which input failed when the test breaks. A parameterised table makes the full input/output contract visible at a glance and is consistent with the team's stated preference.

```suggestion
describe("resolveGatewayProduct", () => {
  it.each([
    { isInternal: false, originProduct: undefined, expected: "posthog_code" },
    { isInternal: undefined, originProduct: undefined, expected: "posthog_code" },
    { isInternal: false, originProduct: "signal_report", expected: "posthog_code" },
    { isInternal: true, originProduct: undefined, expected: "background_agents" },
    { isInternal: true, originProduct: "session_summaries", expected: "background_agents" },
    { isInternal: true, originProduct: "signal_report", expected: "signals" },
  ])(
    "isInternal=$isInternal originProduct=$originProduct → $expected",
    ({ isInternal, originProduct, expected }) => {
      expect(resolveGatewayProduct({ isInternal, originProduct })).toBe(expected);
    },
  );
});
```

_{Reviews (1): Last reviewed commit: "feat(agent): forward task_id, task_run_i..." | Re-trigger Greptile}