feat: forward debuggee stdout/stderr to the MCP client (#218)

[debugmcpdev]

Fixes #218.

Problem

A debugged program's stdout/stderr never reached the MCP client. DAP output events flowed intact from the adapter → minimal-dap → proxy worker (IPC dapEvent) → ProxyManager.handleDapEvent, which re-emitted them on the generic 'dap-event' channel — and died there: SessionManagerCore.setupProxyEventHandlers registers handlers for 8 events, none of them 'dap-event', so Node's EventEmitter silently discarded every output event. Python has emitted these events all along (redirectOutput: true); they were simply dropped on the last hop.

What this PR does

1. Typed output event (src/proxy/proxy-manager.ts, src/dap-core/handlers.ts)
output gets a first-class entry in ProxyManagerEvents and its own case in both switch statements (ProxyManager and the functional-core mirror), consistent with stopped/continued/terminated/exited. Other unhandled events still ride 'dap-event'.

2. Per-session capture (packages/shared, src/session/)

• SessionOutputEntry model type (seq, category, output, timestamp, truncated?).
• OutputRingBuffer (src/session/output-buffer.ts): monotonic seq from 1, cap 1000 entries with eviction + dropped count, 8 KB per-entry truncation, renderText() verbatim transcript.
• SessionManagerCore (now an EventEmitter) registers a ninth proxy-event handler that pushes output events into session.outputBuffer — created fresh per launch/attach, alongside the lastStop reset — and emits 'output-captured'. telemetry (js-debug noise) is filtered at write time; a missing category defaults to console per DAP. The handler rides the existing handlers map, so teardown is automatic.

3. get_output tool (src/server.ts)
Cursor-based read: sessionId, optional since (pass nextSince from the previous response) and limit (default 100, max 1000). Returns { entries, nextSince, hasMore, dropped }. Deliberately does not validateSession() — reading output after the program finished is the primary use case; the buffer stays readable until close_debug_session. since/limit are registered in the SSE arg-coercion map (and sinceTimestamp, a pre-existing gap, is registered while touching that map).

4. Output resources + subscriptions (src/server.ts)
Each session exposes debug://sessions/{id}/output (text/plain, verbatim interleaved transcript). Server capabilities now declare resources: { subscribe: true, listChanged: true }; resources/list|read|subscribe|unsubscribe are implemented, list_changed fires on session create/close, and resources/updated pings are debounced (~150 ms per URI) so notification volume is independent of how fast the debuggee prints. Timers and the SessionManager listener are torn down in stop() (leak-guard safe). The dev proxy passes resource requests through and relays resource notifications (backend restarts drop subscriptions — documented inline).

Adapter audit (from #218's "worth an audit" note)

Adapter	Debuggee output via DAP events	Evidence
Python	✅	235 recorded DAP traces; redirectOutput: true
JavaScript	✅	206 traces (outputCapture: 'std'; telemetry filtered)
Java	✅	JdiDapServer.java pumps both streams
Go / .NET	likely ✅	console: 'internalConsole' path, no traces in-repo
Rust	❓	sets console: but CodeLLDB wants terminal: → #223
Ruby	❌	debuggee stdio goes to the rdbg adapter process → #222
Mock	❌ (by design)	never emits output; unit tests drive the mock ProxyManager

Verification

• Unit: 2529 pass, including new suites for the ring buffer, capture behavior (entry auto-continue window, telemetry filter, re-launch seq reset, post-termination semantics), get_output (incl. TERMINATED-session regression guard), and resources (debounce burst → single ping under fake timers, unsubscribe/stop cleanup).
• E2E (mcp-server-smoke-python): the script's Factorial of 5 print arrives via get_output with category: stdout; cursor round-trip drains; the subscription produced resources/updated; resources/read returns the transcript. Comprehensive matrix gains a lenient per-language get_output row.
• Full suite: 2670 passed; one unrelated JS-attach e2e flaked under full-suite load and passes in isolation.
• Live dogfood through the dev proxy: markers on both streams captured with correct categories and cursor semantics (the exact repro from Debuggee stdout/stderr is never forwarded to the MCP client #218 / the Python interpreter/debugpy probe spawns lack windowsHide: a console window flashes on screen for every session (Windows) #215 comment).

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 95.79832% with 5 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/dap-core/handlers.ts	0.00%	3 Missing ⚠️
src/server.ts	97.40%	2 Missing ⚠️

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