Summary

• New reserved key debugTrace in the build-time defaults override file (alongside optionsButton and runOnInactiveTabs). When true, fresh chrome.storage seeds the debug-trace recorder enabled so the popup's Export button can dump a JSONL trace without a human flipping the toggle. Wired via a new EXTENSION_DEBUG_TRACE_DEFAULT build-time substitution, mirroring the existing options-button-toggle.ts / run-on-inactive-tabs.ts pattern.
• Intended use case: CDP/Browserbase automation that scrapes the IDB-backed trace from a fresh session (e.g. for post-hoc visibility into what the extension touched on each step).
• Adds extension/data/debug-trace.schema.json — JSON Schema (draft 2020-12) describing the union of entries emitted into the JSONL export, mirroring the DebugTraceEntry union in detection-messages.ts. Linked from the README + install docs so downstream consumers can validate.
• README and docs/src/content/docs/install.md updated with the new reserved key and a pointer to the export schema. Example overrides file gets a debugTrace line so the knob is visible.

Test plan

• bun run check (extension/) — biome + eslint clean
• bun run test (extension/) — full suite, 1885 tests pass, including 4 new loadDefaultOverrides cases and 4 new debugTraceStorage env-default cases (mirrors optionsButtonStorage pattern)
• pre-commit run on touched docs/JSON — mdformat reflowed install.md once, then passed on re-run
• bun run build --defaults <{"debugTrace":true}> — verified the substituted bundle contains const raw = "true"; inside resolveDefault() and the storage seeded to true for fresh installs; default build (no override) still seeds false
• Smoke-test in Chrome: load the override'd dist/, open the popup on a fresh profile, confirm "Debug trace" checkbox starts ticked and exports JSONL

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