fix(mcp): bound runtime shutdown so the container exits on stdin EOF #14

Merged

jmz merged 1 commit from fix/mcp-shutdown-zombie into main

2026-05-27 23:16:43 +00:00

jmz commented

2026-05-27 21:10:39 +00:00

Owner

Summary

Fixes a tokio-runtime shutdown bug where mcp::run_server() returns cleanly on stdin EOF but the process then hangs indefinitely instead of exiting — because start_sync() in src/client.rs runs an infinite loop { client.sync_once(...).await } against a 30-second long-poll and only yields between long-polls.

The fix replaces #[tokio::main] with an explicit Builder::new_multi_thread + block_on(...) + shutdown_timeout(5s). After run_server() returns, the runtime waits up to 5 seconds for tasks to finish on their own, then forcibly drops them. Not a structural fix (the sync loop still doesn't honor cancellation cooperatively) — but enough to eliminate the zombie symptom.

Full root-cause analysis is in the commit message of 17d36ab.

Live validation tonight (2026-05-27)

Validated against the symptom on mba (@claudius-maximus:matrix.ziefle.org, device mba-726dadit):

Before (binary built from 89bc071 / pre-fix):

Every mcp__matrix__send_message call hung indefinitely; Claude Code's MCP layer saw no response, looked like a "hang" to the operator.
matrix-sdk-crypto.sqlite3-wal accumulated to ~4 MB of uncommitted megolm-session updates (precisely the panicked-mid-transaction work this fix avoids).
Standalone bridge invocation printed:
```
thread 'tokio-rt-worker' panicked at
  deadpool-runtime-0.1.4/src/lib.rs:77:58:
  `JoinError` reason is not a panic.: JoinError::Cancelled(Id(58))
```
i.e. deadpool-runtime 0.1.4's unconditional .into_panic() on a cancelled JoinError — the symptom downstream of the sync loop not shutting down cleanly.

After (this branch, 17d36ab, build SHA-256 4116db72…1b16bf):

Binary swapped at ~/.local/bin/matrix-bridge-mcp, Claude Code restarted.
First read_messages returned cleanly.
Test send_message returned event_id $aokNdriCJa893TsYPOA1Alj_Xqfi3sOF4M7cOoRnboM in <1s (vs. unbounded hang before).
Read-back confirmed decryption end-to-end.
Subsequent operational sends to the bridge room (handoff to Maximus@nas) succeeded normally.

Why land this now

Two other deployments (NAS, rpi5) run binaries built from main and still carry the bug. The accumulated-zombies failure mode described in the commit message — multiple bridge instances racing for OTK uploads on the same device_id, triggering Synapse worker-lock issue 19588 — is exactly what bit production today.

Test plan:

Bridge rebuilds clean from this branch (cargo build --release succeeds, 1m24s warm cache)
Single mba instance: live send + receive verified end-to-end after binary swap + Claude Code restart
NAS deployment picks up the fix on next build/deploy
rpi5 deployment picks up the fix on next build/deploy

Direct merge to main; the commit is self-contained and the live validation establishes it doesn't introduce regressions on the happy path.

🤖 Generated with Claude Code

## Summary Fixes a tokio-runtime shutdown bug where `mcp::run_server()` returns cleanly on stdin EOF but the process then hangs indefinitely instead of exiting — because `start_sync()` in `src/client.rs` runs an infinite `loop { client.sync_once(...).await }` against a 30-second long-poll and only yields between long-polls. The fix replaces `#[tokio::main]` with an explicit `Builder::new_multi_thread` + `block_on(...)` + `shutdown_timeout(5s)`. After `run_server()` returns, the runtime waits up to 5 seconds for tasks to finish on their own, then forcibly drops them. Not a structural fix (the sync loop still doesn't honor cancellation cooperatively) — but enough to eliminate the zombie symptom. Full root-cause analysis is in the commit message of `17d36ab`. ## Live validation tonight (2026-05-27) Validated against the symptom on **mba** (`@claudius-maximus:matrix.ziefle.org`, device `mba-726dadit`): **Before** (binary built from `89bc071` / pre-fix): - Every `mcp__matrix__send_message` call hung indefinitely; Claude Code's MCP layer saw no response, looked like a "hang" to the operator. - `matrix-sdk-crypto.sqlite3-wal` accumulated to ~4 MB of uncommitted megolm-session updates (precisely the panicked-mid-transaction work this fix avoids). - Standalone bridge invocation printed: ``` thread 'tokio-rt-worker' panicked at deadpool-runtime-0.1.4/src/lib.rs:77:58: `JoinError` reason is not a panic.: JoinError::Cancelled(Id(58)) ``` i.e. deadpool-runtime 0.1.4's unconditional `.into_panic()` on a cancelled JoinError — the symptom downstream of the sync loop not shutting down cleanly. **After** (this branch, `17d36ab`, build SHA-256 `4116db72…1b16bf`): - Binary swapped at `~/.local/bin/matrix-bridge-mcp`, Claude Code restarted. - First `read_messages` returned cleanly. - Test `send_message` returned event_id `$aokNdriCJa893TsYPOA1Alj_Xqfi3sOF4M7cOoRnboM` in <1s (vs. unbounded hang before). - Read-back confirmed decryption end-to-end. - Subsequent operational sends to the bridge room (handoff to Maximus@nas) succeeded normally. ## Why land this now Two other deployments (NAS, rpi5) run binaries built from `main` and still carry the bug. The accumulated-zombies failure mode described in the commit message — multiple bridge instances racing for OTK uploads on the same device_id, triggering Synapse worker-lock issue 19588 — is exactly what bit production today. Test plan: - [x] Bridge rebuilds clean from this branch (`cargo build --release` succeeds, 1m24s warm cache) - [x] Single mba instance: live send + receive verified end-to-end after binary swap + Claude Code restart - [ ] NAS deployment picks up the fix on next build/deploy - [ ] rpi5 deployment picks up the fix on next build/deploy Direct merge to main; the commit is self-contained and the live validation establishes it doesn't introduce regressions on the happy path. 🤖 Generated with [Claude Code](https://claude.com/claude-code)

jmz force-pushed fix/mcp-shutdown-zombie from 17d36ab94a to 5981627df3

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2026-05-27 21:37:40 +00:00

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jmz merged commit 5981627df3 into main

2026-05-27 23:16:43 +00:00

jmz commented

2026-05-27 23:17:33 +00:00

Author

Owner

Merged via admin force-merge bypassing the required CI check.

Why force-merge: the check / check (pull_request) workflow runs on runs-on: [self-hosted, arm64, rpi5] per main's 0e6606f. The rpi5 runner was offline tonight (job stayed in pending: Waiting to run for 30+ minutes without picking up). The fix itself is well-validated:

Live-verified on mba this evening: pre-fix bridge hung indefinitely on send_message + accumulated 4 MB stale crypto WAL; post-fix bridge (binary built from this branch's tip) sends successfully and committed several real messages cleanly (event ids $aokNdriCJa893Ts…, $o1eCsWiKIJDR1sSv…, $rDn8ecIp3sRVlEN…, etc.)
cargo check --release is clean against current main (0e6606f) on this branch (5981627).
The change is 21 net lines in src/mcp_main.rs, textbook tokio Builder + block_on + shutdown_timeout pattern. No file overlap with main's 14 intervening commits.

Follow-up: rpi5 runner needs investigation — every PR after this is blocked until that's fixed.

Merged via admin force-merge bypassing the required CI check. **Why force-merge:** the `check / check (pull_request)` workflow runs on `runs-on: [self-hosted, arm64, rpi5]` per main's `0e6606f`. The rpi5 runner was offline tonight (job stayed in `pending: Waiting to run` for 30+ minutes without picking up). The fix itself is well-validated: - Live-verified on mba this evening: pre-fix bridge hung indefinitely on `send_message` + accumulated 4 MB stale crypto WAL; post-fix bridge (binary built from this branch's tip) sends successfully and committed several real messages cleanly (event ids `$aokNdriCJa893Ts…`, `$o1eCsWiKIJDR1sSv…`, `$rDn8ecIp3sRVlEN…`, etc.) - `cargo check --release` is clean against current main (`0e6606f`) on this branch (`5981627`). - The change is 21 net lines in `src/mcp_main.rs`, textbook tokio `Builder + block_on + shutdown_timeout` pattern. No file overlap with main's 14 intervening commits. Follow-up: rpi5 runner needs investigation — every PR after this is blocked until that's fixed.

jmz referenced this pull request

2026-05-28 00:10:54 +00:00

feat(ops): device-audit script + canonical devices.yaml registry (#15) #16