fix(sentry): protect the rootkey by key name, not value shape

[gmaclennan]

Closes #77. Replaces #196.

#196 proposed an exact-shape base64-22 value rule to catch bare (unmarked) rootkey tokens. Stepping back from that design: the value-shape approach hard-codes the wire encoding in places nothing keeps in sync with backend/index.js's validator (and the encoding has changed before — the legacy app stored the key as hex, see LegacyRootKeyDecoder, an encoding a base64 rule structurally cannot match without redacting every trace id). Meanwhile, tracing the key end-to-end shows every realistic leak shape carries the rootKey field name right next to the value: the key exists as a base64 string only inside the init frame (native → control socket → backend); it never enters the RN JS layer at all, and past the init handler it is a Buffer whose accidental serialisations (hex dump, byte array) a base64 rule would not match anyway.

So this PR filters on the key, not the value's shape, and fixes the holes the bare-token rule was compensating for:

1. Marker rule reaches quoted values. The rootKey marker regex now consumes an optional quote after the separator. Previously {"rootKey":"…"} (a logged init frame) and rootKey: '…' (a console.warn'd message object, exactly what util.format produces) both passed through unredacted — verified against the old regex. These are the two realistic leak shapes.
2. Key-named object fields redact regardless of encoding. rootKey/root_key/root-key joins lat/lng in SENSITIVE_KEY_PATTERN, so a structured {rootKey: …} in extra/contexts/breadcrumb data is redacted whatever the value looks like — base64, hex, or anything future. (The walker already did this for coordinates; the rootkey was the inconsistency.)
3. Capture sites stop logging payloads. simple-rpc.js logged the full message object on the invalid-message path — on the very socket the init frame travels — and both simple-rpc.js and comapeo-rpc.js logged the parse Error on messageerror, whose message embeds a snippet of the raw input under V8 ("…{"rootKey":"MDEy…" is not valid JSON). They now log only the frame type / error name. With the debug-only consoleIntegration on, these were the only real paths for a key to reach a Sentry payload.

There is deliberately no value-shape rule for bare unmarked tokens; the decision and its rationale are documented in both scrubber copies and docs/sentry-integration.md §8. The rootkey metric tag-name ban already covers the realistic metrics mistake, so no tag-value scan is added either.

Tests: shared cases in test-support/scrubber-cases.js cover the JSON-quoted, util.inspect-quoted, and root_key-variant forms (and pin that bare tokens still pass, as a deliberate decision); both scrubEvent suites assert key-field redaction works on a hex value to prove encoding-independence; a new simple-rpc test drives real sockets with an unknown-type frame and a truncated init frame each carrying a key and asserts no key material reaches the console.

Verified with npm run lint, npm run build, npm run test (78 passed), npm run backend:test (97 passed), plus a generative check: 1,000 random 16-byte keys through the logged-frame and inspected-object shapes — 0 leaks.

🤖 Generated with Claude Code

https://claude.ai/code/session_01F1HTHPYkoyjjcvLgsUpvMk

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