# Performance Improvements — Job Tracker

**Companion to:** [MEMORY_LEAK_REPORT.md](MEMORY_LEAK_REPORT.md) · [ROOT_CAUSE_ANALYSIS.md](ROOT_CAUSE_ANALYSIS.md)

## Changes made (this pass)
| Change | File | Effect | Verified |
|---|---|---|---|
| **Stop the infinite `/auth/me` request loop** — make `clearAuthClientState` emit `auth-changed` only on a real signed-in→out transition | `job-tracker-ui/src/auth.ts` | Eliminates a runaway request storm (100+ `GET /auth/me` and climbing) that ran continuously whenever the user was logged out | **Runtime-confirmed** in a live stack: `/auth/me` count 100+ & growing → 0 and stable after fix |
| Revoke CV-preview blob URLs on unmount only (ref-based), not on every carousel change | `job-tracker-ui/src/pages/ProfilePage.tsx` | Fixes broken previews on multi-template decks; still frees URLs on unmount | `profile-page.test.tsx` 5/5 |

### Runtime finding — self-triggering auth loop (the most impactful issue found)
Only visible with a running backend (static analysis could not surface it). Sequence: the axios response
interceptor (`api.ts`) calls `clearAuthClientState()` on **every** 401; that dispatched `"auth-changed"`;
the `App` handler re-fetched `/auth/me`; that 401'd again → interceptor → `clearAuthClientState()` →
`"auth-changed"` → … an unbounded loop that hammered the server and spun the client on the login page and
after any session expiry. Fix: `clearAuthClientState` now only emits when it actually removes a stored user
key (idempotent), so repeated 401s can't re-trigger the fetch. This is a CPU/network/battery drain and a
self-inflicted request flood, not a memory leak — but squarely in the Phase 3.5 "infinite polling / retry
loop / duplicate requests" scope, and the single highest-value fix from the whole investigation.

> Context: this was the only defect found in a full resource audit. The codebase already practises
> disciplined cleanup (timers cleared, listeners removed, object URLs revoked), so there was no leak to
> fix — see the main report.

## Recommended (low-severity, optional)

### 1. Stabilise the extraction-run poll — *minor*
`ProfilePage.tsx:315-324` recreates its 4s interval on every poll because `extractionRuns` is in the deps
and changes each tick. It's harmless (cleanup runs; it stops when runs finish) but churns. If touched:
poll on a stable trigger (e.g. a boolean `hasActiveRuns` in deps, or read runs from a ref inside the
interval) so the interval is created once per active-window.

### 2. One live heap-snapshot pass on a populated session — *verification, not a fix*
The static audit is strong, but a single DevTools confirmation closes the loop:
1. Run the real stack (backend on `:5202` + a seeded DB) and sign in.
2. DevTools → Memory → take a heap snapshot.
3. Navigate `/dashboard → /jobs → open a job dialog → close → /profile → build a CV deck → back`, ×5.
4. Force GC, take a second snapshot, **Comparison** view.
5. Expect: node/listener/detached counts return to baseline (sawtooth), not monotonic growth. Sort
   retained size by constructor; look for `Detached HTMLElement`, growing `Array`/`Map`, or listener
   counts that never fall.

Also cheap and useful: `performance.memory.usedJSHeapSize` (Chromium) logged across the loop, or a
Playwright script that repeats the navigation and asserts heap stays bounded.

### 3. Guard async setState after unmount — *defensive, not a current leak*
Several components `await api…().then(setState)`. React 18 no-ops setState on unmounted components (just a
dev warning historically), so this is not a leak, but for long CV/AI calls consider an `AbortController`
on the request (cancels the in-flight network work on unmount) — improves responsiveness and avoids wasted
work more than memory.

## Prevention — keep leaks from creeping in
- **Lint:** enable `react-hooks/exhaustive-deps` (surfaces the exact wrong-deps class that caused the one
  bug here) and consider `react-hooks/react-compiler` checks.
- **Rule of thumb:** any effect that *acquires* a resource (listener, timer, object URL, observer,
  subscription, connection) must return a cleanup that releases exactly that resource. "Release once on
  unmount" ⇒ empty-deps effect + a ref for current state — never a value in the deps array.
- **Object URLs:** pair every `createObjectURL` with a `revokeObjectURL` in the *same* owner; prefer
  revoking on unmount/replace, never on unrelated re-renders.
- **Server caches:** every `IMemoryCache.Set` must carry an absolute/sliding expiration (as
  `GmailOAuthService` correctly does); if the app grows to heavy caching, set a `SizeLimit`.
- **No unbounded static state:** keep `static` collections to fixed lookup tables (as today); never
  accumulate per-request data in a static field.
- **CI:** the heavy RTL suites are timeout-flaky under load — raising `testTimeout` (e.g. 15–20s) or
  reducing jest worker contention would make regressions (including any future leak-guard tests) reliably
  visible instead of hidden behind flakes.

## Security-audit note (standing instruction)
The applied change carries no security surface (client-side URL lifetime only). The recommendations above
introduce none either; if #3 (AbortController) is implemented, ensure aborted requests don't leave
partial writes — not applicable to the read-only CV export/preview calls here.