fix(git): keep task PR state in sync when the primary PR changes

[frankh]

Problem

The #3227 feature let a task carry multiple PRs, with the "primary" PR being whichever URL sits at index 0 of an ordered list. A task's displayed state (merged / open / draft / closed) is a denormalized cache derived from that primary PR.

When a user promotes a different PR to primary (via the "Other PRs" submenu), TaskPrStatusService.setPrimaryPrUrl reordered the URL list but broadcast the old primary's cached prState alongside the new primary's URL. If the old primary was merged and the new primary was still open, every consumer of the taskPrInfoChanged event (sidebar badge, inbox, home, code-review) showed the task as "merged" while its primary PR was actually open. The drift only self-healed up to ~60s later when the next background revalidation poll overwrote the cache.

Root cause: promotePrUrl only rewrites the prUrls JSON column; the prUrl/prState columns are maintained by a separate updatePrCache path driven by revalidation, so the two disagreed until the next poll.

Fix

setPrimaryPrUrl now fetches the promoted PR's live state via gitService.getPrDetailsByUrl + mapPrState (the same primitives computeTaskPrStatus already uses), persists it through updatePrCache, then emits the fresh state. The cache columns and prUrls[0] can no longer disagree, and every taskPrInfoChanged consumer updates immediately rather than on the next poll.

The port signature changed from void to Promise<void>; the tRPC router forward already awaits it transparently.

Non-goals

The reverse scenario (a non-primary PR merging) intentionally leaves task state unchanged, since state is derived only from the primary PR.

Testing

• Replaced the setPrimaryPrUrl test that codified the buggy stale-emit with two tests: one asserting the promoted PR's live state is recomputed and emitted, one covering getPrDetailsByUrl → null yielding prState: null.
• pnpm --filter @posthog/workspace-server test task-pr-status — 7 tests pass.
• @posthog/workspace-server and @posthog/host-router typecheck clean.

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[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit 0ed3219.}

[github-actions]

Small correctness fix: promotes PR URL then fetches live state instead of emitting stale cached state. The interface change from void to Promise<void> is consistent across the interface, implementation, and the single router call site (tRPC mutation handles async natively). No showstoppers.

[greptile-apps]

_{Reviews (1): Last reviewed commit: "fix(git): keep task PR state in sync whe..." | Re-trigger Greptile}

New commits pushed (delta classified non_trivial_delta) — stamphog approval dismissed; re-review running automatically.

[github-actions]

Small correctness fix that fetches live PR state after promoting a URL instead of emitting stale cached data. The .catch(() => null) guards against network failures, and the Promise<void> interface change is handled natively by the tRPC mutation call site. Both reviewer concerns were addressed in the current head.