test(performance): add the J1 launch-to-usable journey benchmark (#1698)

* test(performance): add the J1 launch-to-usable journey benchmark

Implements plan items A1, A3 (J1 only) and the minimal A4 from
.plans/2026-09-25-performance-journeys-ratchet.md.

- journey-renderer-probe.ts: init-script probe counting DOM mutations,
  layout shifts and long tasks until the first source card is visible on
  /workspace with the splash removed; unit-tested with jsdom fixtures.
- journey-main-ipc-capture.ts: counts bridge invocations from the preload's
  renderer-API trace channel up to a sentinel call the probe fires, so the
  IPC counter is exact without touching production code.
- launch.journey.ts + playwright.journeys.config.ts: seeded profile (one
  M3U source, one Xtream portal on the loopback mock), one warm-up and five
  measured iterations, fresh process and data directory each, writing
  dist/performance/journeys/<timestamp>/summary.json with exact counters
  and P50/P90 wall-clock.
- Nx target electron-backend-e2e:journeys and root script perf:journeys.
- docs/architecture/performance-journeys.md, README, context and
  validation map entries.

renderer.cdTicksToFirstCard and main.sqlStatementsBeforeReadyToShow are
reported as unavailable with the reason instead of being faked.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

* test(performance): gate the renderer load so the probes never race startup

Review follow-up for #1698.

- journey-renderer-gate.cjs: a main-process hook loaded with `-r` (the
  mechanism Playwright uses for its own loader) makes the first
  loadFile/loadURL navigate to about:blank and holds the real load until
  the test releases it. Playwright reports no page before a navigation
  commits, so this is what lets the renderer probe be registered on the
  page before the real document exists; the IPC capture is installed
  before the release too. A safety timeout releases the gate on its own
  and marks the iteration invalid. Unit-tested with a fake BrowserWindow.
- launch-journey-app.ts: registers the probe on the parked page, releases
  the gate, waits for the real document to commit, fails fast when the
  probe is missing, and refuses an iteration whose gate timed out, saw a
  second load, or released before the probe was in place.
- journey-renderer-probe.ts: entries delivered live after the terminal
  batch are buffered and filtered by the same cutoff as queued ones, and
  the cutoff is sampled in a timer queued from the first rAF, i.e. after
  the card's frame is painted, so the render task's long task and layout
  shift are consistently included.
- launch-journey-record.ts: layoutShiftScore rounded to three decimals; a
  0.0001 shift flipped in and out of the cutoff between iterations.
- playwright.journeys.config.ts: reuse a mock server left on the journeys
  port locally (its fixtures are deterministic); CI still starts its own.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

* test(performance): validate the journey gate after the probe completes

Codex follow-up on #1698: the gate state returned by release() cannot see a
reload or recovery navigation that happens before the first card. Re-read the
live state once the renderer probe has finished and validate that instead,
so an iteration spanning an extra navigation is rejected.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

* test(performance): fail an iteration whose performance observers were unavailable

Codex follow-up on #1698: a renderer that cannot observe layout-shift or
longtask entries used to pass the probe with zero counters, which a ratchet
could not tell apart from a genuine zero. The probe assertion now rejects
such an iteration and names the missing observer.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

---------

Co-authored-by: 4gray <fourgray@proton.me>
Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

docs/maintenance/agent-context-map.md

@@ -14,7 +14,7 @@ are not prerequisites for reading repository contracts.
 | Bootstrap, project placement, dependencies, aliases and lint configuration; root Nx config and project-local project.json files | [Nx boundaries](../architecture/nx-workspace-boundaries.md), [security overrides](../architecture/dependency-security-overrides.md) | [Nx architecture](../../.codex/skills/iptvnator-nx-architecture/SKILL.md) |
 | Angular conventions; docs and skills maintenance | [Agent workflow](../development/agent-workflow.md) | Use the area's skill below |
 | Unit, E2E, lint and coverage; `tools/coverage` | [Validation map](../architecture/validation-map.md) | Use the area's validation section |
-| Performance journeys, counters and the CI ratchet; `tools/performance` | [Performance journeys](../architecture/performance-journeys.md) | Read the contract directly |
+| Performance journeys, counters, benchmark probes and the CI ratchet; `apps/electron-backend-e2e/src/journeys`, `apps/electron-backend-e2e/src/performance`, `tools/performance` | [Performance journeys](../architecture/performance-journeys.md) | Read the contract directly |
 | Electron entry/events/preload and CDP; `apps/electron-backend` | [Debugging and trace flags](../development/electron-debugging.md), [Electron security](../architecture/electron-security.md) | Use the available global electron skill for automation |
 | Releases, notes, screenshots, native assets, Linux manager metadata; `tools/release` | [Release pipeline](../architecture/release-pipeline.md), [note format](../../.changes/README.md) | [Release notes](../../.codex/skills/release-notes/SKILL.md), [release cut](../../.codex/skills/release-cut/SKILL.md) |