fix(hermes): the bridge child inherits a PATH that can find Bun (v1.50.3) - #176
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A Hermes gateway starts its memory providers with a minimal inherited PATH. The provider coped with that on its own side - the fallback scan in `_find_executable` locates an absolute `~/.local/bin/o2b` that `shutil.which` never sees - and then handed the wrapper to a subprocess that inherited the same tiny PATH. The wrapper's first act is `command -v bun`, which misses, so it exits 127 before writing a byte of JSON-RPC and the handshake dies at EOF. Memory tools stayed advertised from the vendored schemas and every call was refused. Resolve the runtime the same way the command is resolved, and carry it: when PATH cannot see Bun but the scan can, the child is launched with that Bun's directory first on its PATH. The bridge grows an optional `env` for it, and the shared-bridge key grows the search path, because two children launched with different PATHs are different servers. The wrapper branch is now gated on a Bun existing at all. It stays the preferred command - it is what sources the macOS sqlite-vec shim - but preferring it when nothing can satisfy its precheck only buys a command that is guaranteed to exit 127. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_017dYpaSgWTK5L6o6AzcLcBd
The stderr drain existed to keep a chatty child from blocking on a full pipe and read every line into the void. So when `o2b mcp` refused to start, the only thing that reached the gateway log was "unexpected EOF from MCP server" - a true statement about the transport and a useless one about the cause, while `error: 'bun' is not on PATH.` was thrown away one buffer over. Keep the tail instead: the last 20 lines, capped at 8 KiB, appended to the transport error when the handshake fails. The drain stays a daemon thread that never blocks and never grows without bound, and only transport failures are rewritten - a JSON-RPC rejection came from a server that is talking, and its stderr is noise. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_017dYpaSgWTK5L6o6AzcLcBd
The Bun precheck asks `command -v bun` and, on a miss, tells the operator to install a runtime that is already installed. That advice is right for a fresh machine and wrong for the case it actually fires in: a process launched with a minimal inherited PATH, one directory away from the Bun it needs. The o2b-hook wrapper does not source the precheck and repeated the same miss on its own, skipping the hook in silence. Both now look at the standard install location before deciding Bun is absent. Nothing else moves: the version gate still runs against whatever was adopted, and a machine with no Bun anywhere still gets the install instructions and exit 127. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_017dYpaSgWTK5L6o6AzcLcBd
Prefetch reads the structured item bodies of `brain_context_pack` and dropped to the legacy text channel whenever it assembled nothing. An empty pack is a perfectly ordinary answer, though - there was nothing to recall - and the text channel for that same call carries the raw pack JSON, local vault path included, or the transport's preview envelope. Either one lands in the prompt. A server that answered with an `items` key has spoken the structured contract, so its answer stands even when it is empty. The text fallback is reserved for a result that omits `items` entirely, which is the only shape that really is a legacy server. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_017dYpaSgWTK5L6o6AzcLcBd
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_017dYpaSgWTK5L6o6AzcLcBd
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Included review availability: Your plan provides up to 2 included reviews per hour; 0 remain after this review. 📝 WalkthroughWalkthroughThe 1.50.3 release improves Bun discovery and PATH propagation, adds bounded MCP child stderr diagnostics, corrects empty structured context-pack handling, expands tests, and updates version and changelog metadata. ChangesHermes runtime and release updates
Estimated code review effort: 3 (Moderate) | ~25 minutes Merge Risk: ⚪ Minimal · up to The PR improves Bun runtime discovery, child-process diagnostics, and empty-result handling without introducing a supported merge-blocking risk; it is merge-ready after normal checks. Sequence Diagram(s)sequenceDiagram
participant HermesProvider
participant BunResolver
participant McpBrainBridge
participant MCPChild
HermesProvider->>BunResolver: Resolve Bun and build child PATH
HermesProvider->>McpBrainBridge: Request bridge with child environment
McpBrainBridge->>MCPChild: Launch MCP child with environment
🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
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🧪 Generate unit tests (beta)
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Inline comments:
In `@plugins/hermes/bridge.py`:
- Around line 343-377: The _drain_stderr method can retain an unterminated
stderr record at arbitrary size before applying the limit. Replace line-based
reading with fixed-size chunk reads, maintain only a bounded partial-line
buffer, and append complete or final fragments to _stderr_tail while preserving
UTF-8 replacement and tail limits. Add a regression test covering input larger
than STDERR_TAIL_MAX_BYTES without a newline, verifying memory and excerpt
output remain bounded.
In `@tests/scripts/bun-precheck.test.ts`:
- Around line 43-44: Update the restricted-PATH environments in
tests/scripts/bun-precheck.test.ts lines 43-44 and tests/hooks/o2b-hook.test.ts
lines 100-102 to use the same temporary PATH containing only the shell utilities
required by _bun-precheck.sh, excluding /usr/bin and /bin or any host Bun
locations so both tests resolve the test-local ~/.bun/bin/bun.
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.claude-plugin/plugin.json.codex-plugin/plugin.jsonCHANGELOG.mdopenclaw.plugin.jsonpackage.jsonplugin.yamlplugins/codex/.codex-plugin/plugin.jsonplugins/hermes/bridge.pyplugins/hermes/plugin.yamlplugins/hermes/provider.pypyproject.tomlscripts/_bun-precheck.shscripts/o2b-hooktests/hooks/o2b-hook.test.tstests/python/test_memory_provider.pytests/scripts/bun-precheck.test.ts
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Two defects the review found, both in the guarantees this branch claims rather than in what it set out to change. The stderr tail was bounded per line and per line count, but `readline` returns only at a newline or at EOF - so a child emitting one enormous unterminated record was held whole in the parent before any truncation could apply, which is the exact case the buffer exists to rule out. The drain reads fixed-size chunks now and clips the in-progress line as it grows. `read1` is preferred where the stream offers it, because a buffered `read` waits for the full chunk and would hold the excerpt back until the child had said that much more. The two script tests built their restricted PATH from `/usr/bin:/bin`. Neither holds Bun here, but on a machine where a distribution package puts it there the child would resolve that Bun and the PATH repair would go untested. Both now run against a PATH holding only the utilities the scripts reach for, with the absence of Bun asserted rather than assumed. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_017dYpaSgWTK5L6o6AzcLcBd
itechmeat
approved these changes
Aug 22, 2026
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Summary
A Hermes gateway starts its memory providers with a minimal inherited
PATH. On such a deployment the Open Second Brain memory tools were advertised and every call to them was refused, with nothing anywhere naming a cause. Reported as #173.After this change, that operator gets a working memory bridge: the child is launched with a
PATHthat contains the Bun runtime the provider already located. And when the bridge genuinely cannot start, the error carries the child's own words instead of a sentence about the transport.Root cause
Three defects compounded, each individually survivable.
_resolve_command()returned the~/.local/bin/o2bwrapper as soon as the fallback scan found it. That scan exists precisely becausePATHis too small forshutil.which- so the provider knewPATHwas inadequate and handed the wrapper over anyway._default_spawncalledsubprocess.Popenwithoutenv=, so the child inherited the gateway's minimalPATH. The wrapper's first act iscommand -v bun, which missed, and it exited 127 before writing a byte of JSON-RPC.unexpected EOF from MCP server- true about the transport, useless about the cause - whileerror: 'bun' is not on PATH.was thrown away one buffer over.The result an operator saw: memory tools listed from the vendored static schemas, every call refused, and no diagnostic.
What ships
plugins/hermes/provider.py-_resolve_env()NonewhenPATHalready resolves Bun or when no Bun exists; otherwiseos.environwith the discovered Bun's directory first onPATHplugins/hermes/bridge.py-McpBrainBridge(env=...)Popen(env=...). Omitted means inherit, which is the previous behaviourplugins/hermes/provider.py-_shared_bridge_key()PATHs are different servers and must not share one bridgeplugins/hermes/provider.py-_resolve_command()o2bwrapper stays the preferred command - it is what sources the macOS sqlite-vec shim - and is skipped only when no Bun exists anywhere for its precheck to findplugins/hermes/bridge.py-_drain_stderr()/_stderr_excerpt()scripts/_bun-precheck.shcommand -v bunmissing means "not on thisPATH", not "not installed". The standard install location is adopted before Bun is declared absentscripts/o2b-hookplugins/hermes/provider.py-_context_pack_text()itemskey is taken at its word even when the pack is empty. The legacy text fallback is reserved for a result that omitsitems, since that channel carries the raw pack JSON - local vault path included - or the transport's preview envelopeThe version gate in the precheck still runs against whatever was adopted, and a machine with no Bun anywhere still gets the install instructions and exit 127.
Test plan
Every new test was run against the reverted source first and observed to fail: reverting
bridge.pygives 2 errors and 2 failures, revertingprovider.pygives 5 errors and 3 failures, reverting the two scripts gives 3 failing shell-script tests.env HOME=$(mktemp -d) bun test- 11263 pass, 0 fail, 106722 assertions across 1154 filespython -m unittest discover -s tests/python -vwithscripts/onPATH- Ran 135, OK, no skips;test_static_schemas_match_live_tools_listobserved running against the live serverbun run typecheck- cleanbun run lint- 145 warnings, 0 errors, identical to the count onmainbun run fmt:check- all matched files correctly formattedbun run check:paths- cleanbun run sync-version:check- all seven mirrored manifests matchpackage.jsonopenclaw/index.js- identicalEnd-to-end, in the reported shape:
env -i HOME=<throwaway> PATH=/usr/bin:/bin, Bun installed at~/.bun/bin,o2bsymlinked into~/.local/bin.And the diagnostic half, on a throwaway home with no Bun anywhere so the failure is genuine:
Closes #173
Summary by CodeRabbit
New Features
Bug Fixes
Documentation