fix: derive server-backed state instead of mirroring it (Category C, #200)

[JohnRDOrazio]

Stacked on #367, which is itself stacked on #365. Base is fix/set-state-in-effect-category-b, so the diff here is just the Category C change. Retarget down the stack as each merges.

Category C of #200 — server-data-derived state. All three sites.

BranchContext (2 sites)

currentBranch was seeded from the initialBranch prop / sessionStorage pin, then rewritten by two effects: one re-validating it against the branch list every time the query resolved, another applying initialBranch exactly once behind an initialBranchHandled flag.

Both are gone. currentBranch is now a useMemo over the query response and the visitor's explicit selection:

selectedBranch ?? initialBranch ?? storedBranch

Two decisions worth calling out:

Explicit switches are authoritative and not re-validated against the cached list. switchBranch already checks the branch exists, and createBranch selects a branch the server has just created but which the cached list doesn't include until the refetch lands. Only the seeds get validated — which is what the original check was really guarding: a stale pin naming a deleted branch. I got this wrong on the first pass and the existing createBranch test caught it.

initialBranchHandled disappears. It existed to stop the prop being re-applied after the user switched away; the precedence chain says that directly. One nuance: if initialBranch changes before the user has switched, it's now applied, where the old flag ignored anything after the first application. That reads as the more intuitive behaviour for a resume link — flagging it as a deliberate change rather than an accident.

Clearing the stale sessionStorage pin stays in an effect. It writes to sessionStorage and nothing else, so it's synchronisation with an external store, not derived state.

Suggestions page (1 site)

Manual fetch-into-state replaced with a useSuggestionSessions React Query hook shaped like useProject. The hook reports isLoading: false when disabled — a disabled query stays pending forever, which would otherwise spin the page indefinitely for signed-out visitors.

This is the site #200 flagged as overlapping #89; #89's migration (PR #105) is merged, so this was the leftover.

How I verified the BranchContext change

Coverage for the branch-resolution logic was thin, so I wrote eight characterisation tests against the previous implementation first and confirmed they passed before touching anything:

• initialBranch kept when the server confirms it
• sessionStorage pin kept when it still exists
• deleted pin → preferred_branch, and the stale pin cleared
• deleted pin, no preference → current_branch
• preferred_branch ignored when it isn't in the list
• unauthenticated visitors pinned to the default, ignoring any seed
• a user switch surviving a later refetch
• "main" before the server responds

All eight still pass unchanged after the refactor, alongside the 17 pre-existing tests.

Verification against the #367 base

• react-hooks/set-state-in-effect: 9 → 6 warnings.
• npm run type-check clean, npm run lint 0 errors, npm run build succeeds.
• npx vitest --run — 161 files / 2772 tests pass.

Where this leaves #200

With this merged, the only remaining warnings are the four Category D sites in #362, the one #154 removes, and the re-filed app/projects/[id]/editor/page.tsx:311 — which still needs your call on latch-vs-live derivation before it can be done. Once those land the rule can graduate to "error".

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[codecov]

Codecov Report

❌ Patch coverage is 96.29630% with 1 line in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
lib/context/BranchContext.tsx	94.11%	0 Missing and 1 partial ⚠️

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