feat(#271): statement anchors + restart re-resolution (phase 2)

[debugmcpdev]

Summary

Phase 2 of #271: statement anchors — content-addressed breakpoints that recruit the Edit-tool old_string skill agents already practice, instead of the line arithmetic they're demonstrably bad at.

• set_breakpoint {statement: "<exact line text>", nearLine?} — whole-line trimmed-equality match. Ambiguity is an error whose message lists every line: content pair (capped at 20) — the error is the disambiguation UI; nearLine binds to the closest match (ties toward the lower line). Blank/comment-only anchors (#, //, /* — deliberately not bare *, so Rust derefs stay anchorable) and multi-line input are rejected with clear guidance.
• Anchors survive the edit that was the point of the session: the anchor is stored on the breakpoint record (never enters the DAP payload — guard-tested) and restart_debugging re-resolves every anchor against a fresh read of the current file before relaunch, using each breakpoint's previous line to break ties between duplicate statements. Moves are reported in data.anchorResolution.moved; anchors that no longer match keep their previous line and warn (data.anchorResolution.stale + bp.message) rather than failing the restart or silently dropping state.
• Gating: statement/nearLine exist only in content mode (the default) — schema, call handler, server instructions, and workflow prompt all gate together; required drops line there (line addressing remains available). line/assert modes hard-error the params, naming the env value.
• Same readable-file constraint as expectedContent (rejected for Java FQCNs and attach sessions); composes with condition/logMessage/suspendPolicy unchanged.

Builds on #278 (phase 1). Phase 3 (function breakpoints) remains as a capability-gated follow-up.

Testing

• Resolver unit tests: trim/CRLF semantics, multi-match listing + cap, nearLine closest + tie-break, comment heuristic (Rust *deref accepted, #[derive] rejected), multi-line rejection
• Server tests: resolution + anchor storage, ambiguity/no-match/comment errors, param-combination validation (statement×line, statement×expectedContent, bare nearLine), attach/FQCN rejection, assert-mode gating, schema shape per mode
• Session tests: anchor stored; DAP-payload purity guard; restart re-resolution (moved / stale-with-warning / previous-line tie-break / no-anchor purity); breakpoint events preserve requestedLine
• E2E (mock adapter): statement anchor end-to-end; restart re-resolution after a real mid-session file edit (from: 3, to: 5)
• Full suites green: 2901 unit / 6 e2e bp-addressing; lint clean; tsc --noEmit clean

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 92.91339% with 9 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/session/session-manager-operations.ts	89.58%	5 Missing ⚠️
src/skill-content.ts	62.50%	3 Missing ⚠️
src/server.ts	97.14%	1 Missing ⚠️

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