feat(analytics): tag discuss-launched task events with signal_report_id

[andrewm4894]

Summary

Tags discuss-launched sessions with signal_report_id so a session's PostHog events can be filtered down to a single inbox report.

• Renderer: Task created is tagged at both call sites; a super-property (setActiveTaskAnalyticsContext) tags the rest of the in-task renderer events and is cleared on navigation away.
• Agent → LLM gateway: configureEnvironment forwards x-posthog-property-signal_report_id, which the gateway lifts onto $ai_generation events. No posthog-repo change needed — the gateway already lifts arbitrary x-posthog-property-* headers.

Caveat

Only the Anthropic path forwards the header (ANTHROPIC_CUSTOM_HEADERS); OpenAI/codex models won't be tagged.

Test plan

• typecheck, lint, agent + renderer unit tests
• Verified live: renderer events tagged in-task and cleared on navigating to the inbox; gateway already lifts x-posthog-property-task_id onto $ai_generation (the same path this PR adds signal_report_id to)
• $ai_generation carrying signal_report_id — verify post-deploy; discuss runs a prebuilt sandbox agent, so it isn't locally testable

[greptile-apps]

Prompt To Fix All With AI

Fix the following 2 code review issues. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 2
apps/code/src/renderer/stores/navigationStore.test.ts:19-22
**New behavior not tested**

`setActiveTaskAnalyticsContext` was added to the mock to prevent import errors, but no test cases were added to verify it is actually called — or called with the right argument — when navigating to/from a task that has `signal_report` set. Without these tests, a future refactor could silently stop tagging events and the suite would still pass. Consider adding a parameterised test that: (1) navigates to a task whose `signal_report` is populated and asserts `setActiveTaskAnalyticsContext` was called with that task, and (2) navigates back/away and asserts it was called with `null`.

### Issue 2 of 2
apps/code/src/renderer/utils/analytics.ts:160-170
**Stale super-property on cold start**

`posthog.register` persists super-properties to local storage, so `signal_report_id` survives an app restart. On the next launch, the store is rehydrated from persisted state before `hydrateTask` calls `navigateToTask` (which eventually re-invokes `setActiveTaskAnalyticsContext`). Events fired in that window — e.g. the initial `TASK_VIEWED` call or any session-level captures — would carry the `signal_report_id` from the previous session. The gap is small in practice, but worth a call to `posthog.unregister("signal_report_id")` during `initializePostHog` so the slate is always clean at startup.

_{Reviews (1): Last reviewed commit: "feat(analytics): tag discuss-launched ta..." | Re-trigger Greptile}

[chatgpt-codex-connector]

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