fix(gateway): harden Honcho cache memo invalidation

[lkz-de]

Summary

Harden the Honcho cache-busting memo key so coarse-mtime rewrites of honcho.json cannot reuse stale parsed identity state.

Why

On coarse-mtime filesystems, rapid rewrites of honcho.json can keep the same st_mtime_ns while changing contents. The earlier size-only approach still missed equal-size rewrites. Using a SHA-256 content hash as a discriminator closes that remaining stale-config path.

Scope

• memo/cache invalidation only
• no Honcho config schema changes

Test plan

• pytest tests/gateway/test_agent_cache.py
  • includes a regression that forces equal st_mtime_ns, equal file size, changed honcho.json content, and asserts the Honcho parse is refreshed
  • 79 passed locally against the current head

Related

• fix(gateway): bust cache on auxiliary compression changes #39284 — adjacent gateway cache-busting (auxiliary compression); this PR adds an independent Honcho config identity discriminator.

[tonydwb]

Code Review Summary

Verdict: Approved

Fixes Honcho cache memo invalidation: the cache key now includes a component that changes when the config path changes, ensuring cached values don't persist across config reloads.

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Reviewed by Hermes Agent

[teknium1]

Thanks for isolating this to the Honcho memo key. The current-head premise is real: gateway/run.py:15777-15794 keys the memo only by (path, st_mtime_ns), so a coarse-mtime rewrite can reuse the prior parsed identity mapping.

Problems

• Adding st_size detects only size-changing rewrites. Equal-size changes to values consumed at gateway/run.py:15787-15792 remain indistinguishable when mtime is unchanged, so the general stale-config failure remains possible.
• The PR diff has no test. tests/gateway/test_agent_cache.py:349-388 covers a normal rewrite but does not force equal mtime or assert size-key invalidation.

Suggested changes

• Use a discriminator that covers equal-size content changes, or narrow the stated guarantee to size-changing edits.
• Add a regression test with controlled equal st_mtime_ns values and changed config content; assert the parser/cache result is refreshed.

Automated hermes-sweeper review.

[lkz-de]

Thanks — I pushed 2a267da7, which addresses both issues from your review.

The memo key now includes a SHA-256 content-hash discriminator alongside st_mtime_ns / st_size, so equal-size rewrites of honcho.json no longer reuse stale parsed state when st_mtime_ns is unchanged.

I also added a regression in tests/gateway/test_agent_cache.py that forces equal st_mtime_ns, equal file size, changed config content, and asserts the Honcho parse is refreshed.

[teknium1]

Closing after review against current main.

The memo this hardens exists to avoid I/O on the gateway's hot agent-cache path — and adding a full SHA256 of honcho.json to the key means every lookup now reads and hashes the file, which defeats the memo's purpose. The edge it protects against (a same-size rewrite landing inside one mtime tick on a coarse-mtime filesystem) is real but vanishingly rare, and its worst outcome is one stale cache generation until the next change.

If this ever bites someone in practice, the right-shaped fix is size-only: st_size comes free from the stat() call the memo already makes, catching most same-tick rewrites with zero added I/O. Content hashing on the hot path is the part we're declining.

Thanks for the well-tested submission @lkz-de — the failure mode analysis was solid.