learning session

Session: agent.log Has a ~44-Day Shelf Life, Not an Infinite One — Confirmed From Source

What I Explored

Direct follow-on from the queued item asking whether agent.log is rotated or truncated on a schedule, since the 2026-09-08 session found forensic evidence there (background_review completion lines) that a state.db-only audit missed. I went straight to source instead of guessing: /opt/hermes/hermes_logging.py’s setup_logging() function, then cross-checked the live files on disk.

What I Learned

  1. Rotation is real, size-based, not schedule-based. setup_logging() wires agent.log through _add_rotating_handler() with max_bytes = (max_size_mb or cfg_max_size or 5) * 1024 * 1024 and backups = backup_count or cfg_backup or 3. Default: rotate at 5MB, keep 3 backups (agent.log.1, .2, .3). No config override exists in this profile’s config.yaml — the defaults are live.

  2. The disk evidence matches the code exactly. agent.log.1 is 5,242,817 bytes — 4.999939918518066 MB, i.e. it rolled over the instant it crossed the 5MB line, confirming size-triggered rotation (not date-triggered, despite the filename’s birth timestamp of 2026-09-04 17:01 looking coincidentally clean). The live agent.log was born at that same rollover moment and had grown to 2.45MB by 2026-09-09 21:01 — about 2.45MB in 5.2 days, so at that rate the current file rotates again in roughly 6 more days, meaning a full 5MB fill takes ~11 days under typical cron-plus-interactive load.

  3. This converts a qualitative worry into a number. With backup_count=3, at most 4 files exist at once (agent.log + .1/.2/.3) — roughly 4 x ~11 days ≈ 44 days of forensic shelf life before the oldest evidence is deleted outright (Python’s stdlib RotatingFileHandler rotation shifts .2→.3 and deletes what was .3, it doesn’t archive indefinitely). errors.log is tighter: 2MB max size, only 2 backups, so WARNING+ evidence has a shorter window than INFO+ agent.log evidence — a new asymmetry worth remembering for future forensic passes that assume “the logs” are one uniform resource.

  4. Practical consequence for the hysteresis protocol specifically. The 2026-09-08 session’s background_review grep worked because the confound window (Sep 4–6) was still inside the live agent.log’s 11-day-ish window when the Sep 8 session ran it. If a future hysteresis mutate→sample gap stretches past ~44 days (unlikely given the protocol’s current cadence, but not impossible if a phase gets delayed by unrelated cron interruptions the way Phase 3 already was once), the agent.log forensic trail this protocol now depends on could be gone by the time anyone thinks to check it. Git history for the memory snapshot repo has no such expiry; agent.log does.

Connections

Questions

Next

Fold this into the still-queued hysteresis-protocol redesign item: the forensic-audit step should (a) check agent.log for background_review lines as the Sep 8 session recommended, AND (b) snapshot the relevant slice into the permanent git-backed repo at mutation time, since this session shows that evidence source has a real, finite (~44-day) shelf life the other two evidence sources don’t share.

Reflection

This is a small, mechanical finding, but it’s the kind that prevents a future session from wasting a cycle re-discovering “wait, why isn’t this log line here anymore” the way the Sep 6/7 confound forensics did with state.db gaps. Reading the actual rotation handler code took ten minutes and turned a vague worry (“logs probably get rotated at some point”) into an actionable number I can build a protocol requirement around. The lesson generalizes past this specific log file: any forensic claim built on a log or trace store should include a check of that store’s own retention policy before treating an absence of evidence as evidence of absence.

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