fix(engine): honor producer BeginFrame disable env

[miguel-heygen]

Summary

Fixes the producer/browser-crash root cause by making the engine honor the existing production env knob:

• PRODUCER_ENABLE_BEGIN_FRAME=false|off|0 now resolves to forceScreenshot=true
• PRODUCER_FORCE_SCREENSHOT=true remains the direct screenshot-mode knob
• explicit resolveConfig({ forceScreenshot }) overrides still win over env defaults

Production evidence

The failing Temporal activities surfaced as browser/session failures:

• Navigation timeout of 60000 ms exceeded
• Navigating frame was detached
• Protocol error (Runtime.evaluate): Target closed

Root finding from prod:

• temporal-hyperframes-producer-worker-sidecar-configmap already sets PRODUCER_ENABLE_BEGIN_FRAME=false
• every inspected producer sidecar process had PRODUCER_ENABLE_BEGIN_FRAME=false in PID 1 env
• the shipped sidecar bundle only read PRODUCER_FORCE_SCREENSHOT; it did not read PRODUCER_ENABLE_BEGIN_FRAME
• prod logs still showed captureMode:"beginframe" and forceScreenshot:false
• the failed pod had fresh Chrome core files at the exact failure minute, plus defunct chrome-headless children

So prod was configured to avoid BeginFrame, but the engine ignored that compatibility env and kept taking the BeginFrame path.

Verification

• bun test packages/engine/src/config.test.ts packages/engine/src/services/frameCapture-transientErrors.test.ts packages/producer/src/services/render/stages/probeStage.test.ts — 58 pass, 0 fail
• bunx oxfmt --check packages/engine/src/config.ts packages/engine/src/config.test.ts
• bunx oxlint packages/engine/src/config.ts packages/engine/src/config.test.ts
• git diff --check
• pre-commit hooks passed: lint, format, fallow audit, typecheck, commitlint
• direct probe: PRODUCER_ENABLE_BEGIN_FRAME=false now returns resolveConfig().forceScreenshot === true
• direct probe: PRODUCER_ENABLE_BEGIN_FRAME=true keeps forceScreenshot === false

I also pulled the exact failed production artifacts and rendered all three locally through the built CLI with PRODUCER_ENABLE_BEGIN_FRAME=false; all selected screenshot mode and completed:

• nav-timeout-23c1 — rendered successfully
• frame-detached-1a80 — rendered successfully
• target-closed-40c8 — rendered successfully

Deploy / rerun plan

After a producer sidecar image with this patch is deployed, reset or rerun the failed Temporal workflows to verify they no longer hit the browser crash path. I did not reset them before this deploy because current prod would still run the old sidecar image and old config behavior.

[miguel-heygen]

Closing this as the wrong root-fix direction. The investigation evidence showed the prod compatibility env is stale/dead, but James clarified BeginFrame is the preferred Linux path and this env flag is intentionally not the approach we want to use. Continuing investigation at the BeginFrame/browser lifecycle layer instead.