feat: logpoints — set_breakpoint logMessage logs without pausing (fixes #235)

[debugmcpdev]

Closes #235. Builds on #267 (#236).

Logpoints are the prod-safe just-in-time diagnostics primitive: plant them at suspect lines, let the program run at full speed, and read interpolated values from get_output — no pauses, no pre-instrumented logging. This also closes the doc–reality gap where docs/javascript/README.md documented a logMessage parameter that never existed.

What's new

set_breakpoint accepts an optional logMessage (DAP SourceBreakpoint.logMessage, {expr} interpolation). The adapter logs instead of pausing; messages flow through the existing #218/#224 output-capture path into get_output and the debug://sessions/{id}/output resource. condition combines with logMessage per DAP semantics. Logpoints appear in list_breakpoints distinguished by their logMessage field.

Capability gating (hybrid, static-first). New AdapterPolicy.supportsLogPoints (python/js/go/rust/mock true, java/dotnet false, ruby unknown):

• Known-unsupported adapter → fast, clear UnsupportedFeatureError at set time (also when live capabilities post-launch deny it).
• Known-supported → accepted.
• Unknown (ruby) → accepted with a warning, then re-checked against the adapter's live initialize capabilities at launch — mirroring the [FEATURE] Capture adapter initialize capabilities + best-effort exceptionInfo enrichment on exception stops #243 exception-filter drift pattern; a drifting logpoint gets its stored message annotated ("may pause instead of logging").

Pipeline fix underneath: one mapper, four construction sites

There were four independent places building setBreakpoints arrays, each mapping its own subset of fields (suspendPolicy already demonstrated the bug class — it silently vanished on every launch). A single shared toSourceBreakpoint in @debugmcp/shared now feeds all four (SessionManager live re-send, worker initial breakpoints, connection-manager helper, js-debug handshake), and initialBreakpoints carries logMessage/suspendPolicy end-to-end with message-parser validation.

⚠️ Intentional behavior change riding along: launch-time suspendPolicy is now honored for Java instead of silently dropped.

Mock adapter

Simulates logpoints for hermetic e2e: advertises supportsLogPoints, retains logMessage on stored breakpoints, and its run simulation emits output events (naive {expr} interpolation) instead of stopping at logpoint lines — shared walk for both launch and continue paths.

Tests

• TDD units at every layer: shared mapper (key-omission semantics), session store/live-send/initialBreakpoints snapshot, message-parser accept/reject, connection-manager mapping, worker forwarding, js-debug handshake mapping, server gating (all four verdicts), and the launch-time capability drift annotation.
• E2E: new tests/e2e/mcp-server-logpoints.test.ts, language-parameterized across all 8 adapters — python/javascript/go/rust/mock log without pausing (verified against the real adapters); java/dotnet fail fast; ruby warns. 8/8 pass locally. Python additionally asserts real interpolation (LP-MARK a=1).
• Dogfooded live via the dev proxy: a logpoint on fibonacci.py's iteration line streamed LOGPOINT a=0 b=1 → a=21 b=34 into get_output while the program ran to completion, never pausing.

Docs

tool-reference (logpoints section + adapter support matrix), docs/javascript/README.md (the phantom example is now true), jit-diagnostics README (non-breaking inspection pattern), both skill copies + all per-language references, CHANGELOG.

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 97.72727% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/server.ts	95.83%	1 Missing ⚠️

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