bot-bottle/docs/prds/prd-new-audit-event-schema.md

PRD prd-new: Canonical tamper-evident audit-event schema and local query contract

• Status: Draft
• Author: didericis-claude
• Created: 2026-07-26
• Issue: #487

Summary

bot-bottle already emits security- and provenance-relevant events from several producers — supervise operator decisions (PRD 0013's AuditStore), egress allow/block enforcement, git-gate push decisions, control-plane token minting, and (next) host-controller lifecycle transitions — but each writes its own shape to its own sink. There is no shared envelope, no tamper-evidence, and no single place to search. Local incident reconstruction means grepping several stores that don't agree on field names, timestamps, or how a bottle is identified.

This PRD defines one canonical audit-event contract every producer emits into:

1. A versioned envelope — schema version, event id, event type, monotonic + wall-clock timestamps, and an explicit trust boundary between host-supplied and agent-claimed fields.
2. Canonical JSON serialization + a per-writer hash chain, so any deletion or edit of a past record breaks the chain and is detectable offline.
3. An append-only JSONL journal as the source of truth, with a rebuildable SQLite index for local search — no paid platform, no network dependency.
4. An initial event registry covering lifecycle, decision, egress, auth, and forge events.

It is explicitly scheduled to land immediately after the host controller (#468) so the host controller's lifecycle transitions are the first producer wired onto the new contract (per the directive on #487).

Problem

Audit infrastructure is fragmented across #468, #324, and #480 with no shared schema. Concretely:

• No shared envelope. supervise_audit_entries (PRD 0013) has timestamp, bottle_slug, component, operator_action, .... The egress proxy and git-gate log their own ad-hoc lines. There is no common event_id, event_type, or version, so cross-producer correlation ("what did bottle X do between its start and this rejected push?") is manual and lossy.
• No tamper-evidence. The audit store is a plain SQLite table. Anyone who can write the DB can delete or rewrite a row and leave no trace. Audit that an attacker (or a buggy agent) can silently rewrite is not audit.
• Trusted and untrusted data are mixed. A bottle is attributed by source IP → slug at the gateway (host-supplied, trustworthy). An agent can also claim things about itself in a tool call (agent-claimed, adversarial). Today nothing in the record marks which is which, so a reader can be misled by an agent-supplied field that looks authoritative.
• No local search. Reconstructing an incident means reading multiple sinks with different schemas. There is no query contract and no promise that the index can be rebuilt from the journal if it drifts or is lost.
• No redaction rule. Nothing prohibits a producer from writing a raw token or secret into an audit record, which would turn the audit log itself into a credential store.

Goals / Success Criteria

• A single AuditEvent envelope type, versioned, that every producer emits. Fields are split into a trusted block (host-supplied: bottle slug from source-IP attribution, host wall-clock, producer identity) and an untrusted block (anything the agent or a remote claimed), and the split is structural, not a convention.
• Canonical serialization (sort_keys, (",", ":") separators, UTF-8, ensure_ascii=False) is defined once and reused, so the same logical event always hashes identically across producers and hosts.
• Each writer maintains a hash chain: hash = sha256(prev_hash || canonical(event)). Deleting or editing any past record breaks every subsequent link; a standalone verifier detects the break offline with no secret material.
• The JSONL journal is the source of truth; the SQLite index is fully rebuildable from it (audit rebuild reconstructs the DB and re-verifies the chain).
• Local query works with no paid platform and no egress: filter by bottle, event type, time range, and producer, and follow a bottle's events in order.
• A redaction rule is enforced at the envelope boundary: known credential-shaped fields are rejected/redacted before a record is written; the writer refuses raw secrets rather than storing them.
• The host controller (#468) emits lifecycle.* events through this contract as the first consumer; existing supervise/egress producers are migrated behind the same envelope without changing operator-facing behavior.

Non-goals

• Cross-host aggregation / shipping. This PRD makes each host's journal canonical and correlatable by construction (stable ids, hash chain), but the transport that merges multiple hosts into one timeline is a follow-up (#324). The schema is designed so that merge is a later append, not a reformat.
• Cryptographic signing / external anchoring. Hash-chaining gives tamper-evidence (you can detect edits), not tamper-resistance against an attacker who can rewrite the whole chain. Per-writer signing keys and periodic external anchoring are a follow-up; the chain-head hash is the seam they attach to.
• Real-time alerting / SIEM rules. Query is local and pull-based here.
• Retention / rotation policy. Journal rotation and TTL are operator policy, tracked separately; the format must survive rotation (chain head carried across segments) but this PRD does not set the schedule.
• Replacing PRD 0013's operator queue. The supervise proposal/response queue is unchanged; only its terminal audit record is re-emitted onto the new envelope.

Design

The envelope

One dataclass, AuditEvent, serialized to a JSON object with a small, stable top level:

{
  "v": 1,                          // schema version (integer, bumped only on breaking change)
  "id": "<uuid4>",                 // globally unique event id
  "type": "egress.decision",       // dotted event type from the registry
  "seq": 1287,                     // per-writer monotonic sequence (gap-detectable)
  "ts": {
    "wall": "2026-07-26T18:22:04.113Z",  // host wall-clock, RFC3339 UTC (TRUSTED)
    "mono": 90142.55                      // host monotonic seconds since writer start (ordering)
  },
  "producer": "host-controller",   // TRUSTED: which host component wrote this
  "trusted": {                     // host-supplied, authoritative
    "bottle": "amber-fox-12",      // slug from source-IP attribution (may be null for host-level events)
    "host": "mac-studio-1"
  },
  "untrusted": {                   // agent- or remote-claimed; never authoritative
    "reason": "npm install needs registry.npmjs.org",
    "target": "registry.npmjs.org:443"
  },
  "hash": "<hex>",                 // sha256(prev_hash || canonical(this event with hash="" ))
  "prev": "<hex>"                  // hash of the previous record in this writer's chain ("" for genesis)
}

The trusted / untrusted split is the core invariant. A producer may only place a field in trusted if the host established it (source-IP → slug attribution, the host's own clock, the producer's own identity). Everything an agent or a remote said goes in untrusted. A reader (or a future policy engine) can therefore trust trusted.bottle for attribution and treat untrusted.* as adversarial claims — the distinction the current stores lack.

Canonical serialization + hash chain

Serialization is defined once (extends the existing sha256_hex / util.py helpers):

def canonical(event: dict) -> str:
    return json.dumps(event, sort_keys=True, separators=(",", ":"),
                      ensure_ascii=False)

The hash field is computed over the canonical form of the event with hash set to "", prefixed by the previous record's hash:

digest = sha256_hex(prev_hash + canonical({**event, "hash": ""}))

prev is the prior record's hash; genesis uses prev = "". This makes the journal an append-only Merkle-style chain: editing or deleting record n changes its hash, so record n+1's prev no longer matches — the break is local and points at the tampered record. Verification needs only the journal itself (no keys), so it runs offline and in CI.

Journal (source of truth) + SQLite index (rebuildable)

• Journal: one append-only JSONL file per host (path from paths.py, alongside host_db_path()), one canonical event per line, opened O_APPEND. This is authoritative. A single writer per host owns appends (producers hand events to it) so the chain has one well-defined order — the host controller is the natural owner since it already gates the lifecycle.
• Index: a new audit_events table via the existing DbStore / TableMigrations machinery, holding the envelope columns plus JSON blobs, indexed on (bottle, type, wall_ts). It is a derived cache: audit rebuild truncates and replays the journal, re-verifying the chain as it goes. If the DB is deleted or drifts, it is regenerated from the journal with no data loss. (This supersedes the free-standing supervise_audit_entries table, which becomes a view/producer onto the new index.)

Event registry (initial)

Dotted type names, grouped; the registry is a table mapping type → required untrusted keys so producers and the verifier agree on shape:

• lifecycle.* — lifecycle.bottle_start, lifecycle.bottle_stop, lifecycle.bottle_crash (producer: host-controller, #468).
• decision.* — decision.proposed, decision.resolved (producer: supervise; carries operator action + justification, replacing PRD 0013's row shape).
• egress.* — egress.decision (allow/block at the proxy), egress.route_added.
• auth.* — auth.token_minted, auth.token_rejected (control-plane; never the token itself — see redaction).
• forge.* — forge.push_accepted, forge.push_rejected (git-gate), forge.pr_opened.

New types are additive; adding one does not bump v. Removing or re-typing a field bumps v.

Redaction rule

The envelope constructor enforces a deny-list at write time: a field whose key matches known credential shapes (token, secret, password, authorization, *_key, JWT-shaped values) is rejected — the producer must pass a reference (a token id or sha256 fingerprint), never the raw value. auth.token_minted therefore records the token id and role, not the JWT. Redaction is enforced structurally so a producer cannot accidentally write a secret into the audit log.

Implementation chunks

1. (this PR — PRD only.) The contract above. No code; scheduled to land right after #468.
2. Envelope + canonical + chain core. AuditEvent dataclass, canonical(), chain hashing, and the single-writer journal appender in bot_bottle/store/ (reusing sha256_hex); unit tests for determinism, chain-break detection, and redaction refusal.
3. SQLite index + audit rebuild / audit verify CLI. New audit_events migration; replay-from-journal; offline chain verifier; local query commands (by bottle / type / time / producer).
4. Host controller as first producer (#468). Wire lifecycle.* emission into the host controller's start/stop/crash paths.
5. Migrate existing producers. Re-emit supervise decision.* (retiring the standalone supervise_audit_entries shape behind the index), egress egress.*, git-gate forge.*, control-plane auth.*.
6. (follow-up.) Cross-host merge transport (#324); per-writer signing + external anchoring on the chain head; retention/rotation policy.

Open questions

• One writer per host vs. per producer chains. A single appender gives one total order but makes every producer depend on the host controller being up. Alternative: one chain per producer (independent seq/chain head), merged at query time by (wall, mono). Leaning single-writer for v1 (simpler verification, matches the host controller owning lifecycle), with per-producer chains noted as the scaling path. — feedback wanted.
• Monotonic clock across restarts. ts.mono resets when the writer restarts; is seq + wall enough for ordering across a restart, or does the chain need an explicit epoch counter bumped per writer boot? (Leaning: carry the last chain head across restart, so ordering follows the chain, not mono.)
• Redaction: reject vs. redact. Should a credential-shaped field hard- fail the write (surfacing the producer bug loudly) or silently redact to "<redacted>"? Leaning reject in tests / redact in prod behind a flag, so a producer bug can't drop an event entirely in the field.
• Retention interaction with the chain. When an old journal segment is rotated out, the verifier must still trust the current head. Carry the rotated-out head as the new segment's genesis prev? (Tracked with the retention follow-up.)