fix(observe): match interruption markers carried in text blocks

[theonly1me]

What changed

• contentContainsMarker now reads a text block's text field, not only content, via a new blockText helper.
• Added src/observe/adapters/claudeUser.test.ts covering all four markers in three real record shapes: plain string, text block, and tool_result block.

Why

Claude Code carries interruption markers in { type: "text", text: "..." } blocks and denial markers in { type: "tool_result", content: "..." } blocks. The matcher only inspected content, so denials were found and interruptions were not.

Measured on a real corpus of 461 transcripts: 1,033 interruption markers on disk, 4 reaching the index. Denials were unaffected at 447 of 465. The staleness guard in src/signal/health.ts cannot catch this because it requires interruptions and denials to both be zero.

The existing fixture in src/cli/learn.test.ts:56 uses a string content, which is the shape that already worked, so nothing covered the shape that actually occurs.

How to verify

bun run check
bun run cli learn --dry-run

--dry-run runs a full fresh scan into an in-memory database and writes nothing. On the same corpus the mirror goes from 4 interruptions to roughly 1,100, broken down by what was interrupted:

  You stop the agent most often
    while using Bash ................................ 392
    during an explanation ........................... 210
    while using ExitPlanMode ........................ 208
    while using AskUserQuestion ..................... 164
    while using shell_command ....................... 124

Data handling

• Any new capture source has an opt-in flag and a README entry in this PR
• Everything that reaches the network passes redactSecrets
• No raw capture in a log line, an error message, or a test fixture
• A test exercises the real entry point, not just the redaction function

No new source and no new read. This changes which field of an already-parsed record is inspected. Marker classification happens before any TextRef is resolved, so the redaction gate is untouched.