Codex parser: populate TurnRecord.fidelity

[willwashburn]

Context

PR #76 (#41 first cut) introduced TurnRecord.fidelity (granularity + per-field coverage + derived class) and the helpers EMPTY_COVERAGE, classifyFidelity, makeFidelity in @relayburn/reader. The Claude parser populates fidelity on every turn (packages/reader/src/claude.ts:255,1049 via buildClaudeFidelity at :604).

The Codex parser does not. Quoting PR #76's deferred-work paragraph:

Codex and OpenCode parsers (they still emit no fidelity; consumers treat absence as best-effort full for backward compat).

packages/reader/src/codex.ts constructs TurnRecord objects at :513-543 without any fidelity field. As a result, summarizeFidelity (packages/analyze/src/fidelity.ts) buckets every Codex turn under unknown, and hasMinimumFidelity(undefined, …) passes silently — the exact "0 vs unknown" ambiguity #41 was filed to fix.

Proposal

Populate TurnRecord.fidelity in parseCodexSessionIncremental (packages/reader/src/codex.ts) on every emitted turn, mirroring the Claude approach in buildClaudeFidelity.

Coverage for Codex rollouts (event_msg.token_count payload at :283-294):

• hasInputTokens: true — total_token_usage.input_tokens is the source of truth.
• hasOutputTokens: true — total_token_usage.output_tokens.
• hasReasoningTokens: true — reasoning_output_tokens is surfaced; this is one of the few sources where it is.
• hasCacheReadTokens: true — cached_input_tokens.
• hasCacheCreateTokens: false — Codex rollouts have no ephemeral cache-create concept.
• hasToolCalls: true — function_call / custom_tool_call items are captured.
• hasToolResultEvents: true — function_call_output / custom_tool_call_output items are captured (:430-449).
• hasSessionRelationships: false for now — Codex rollouts have no parent-tracking path (per Parity approach: Codex and OpenCode spawn-tagging + incremental ingest without native hooks #63); flip when the spawn-tagging substrate lands.
• hasRawContent: true — full content capture path exists when contentMode === 'full'.

Granularity: 'per-turn'. The cumulative-delta arithmetic in finalizeTurn (:597) gives true per-turn token counts.

If a token-count event is absent for a turn (no task_complete-bound total_token_usage observed before the turn closes), set hasInputTokens / hasOutputTokens / hasReasoningTokens / hasCacheReadTokens to false for that turn so the resulting class is partial rather than a silent zero.

Also follow Claude's pattern of treating hasToolCalls / hasToolResultEvents / hasRawContent as capability flags (true even when a particular turn has no tools), not presence.

Acceptance criteria

• Every TurnRecord emitted by parseCodexSession / parseCodexSessionIncremental carries a fidelity field.
• granularity === 'per-turn'.
• Coverage flags follow the matrix above; hasReasoningTokens is true when a Codex token_count was observed for the turn.
• A turn whose source omitted total_token_usage reports class === 'partial', not 'full', and the missing usage flags are false — usage numeric fields can still be 0 (the existing post-hoc default) but the coverage flag is the honest signal.
• New tests in packages/reader/src/codex.test.ts cover at minimum: a full-fidelity turn (all usage fields present), a turn missing token_count (partial), and a turn with both function_call and function_call_output (tool-result coverage stays true).
• summarizeFidelity over a real Codex session yields unknown === 0 for the produced turns.

Out of scope

• Adopting the same shape in Mux / Crush / other not-yet-built collectors (Collector: Mux (coder/mux) #29, Collector: Crush #30 etc.) — covered by their own issues.
• Wiring hasSessionRelationships to a real signal — that needs the parity work in Parity approach: Codex and OpenCode spawn-tagging + incremental ingest without native hooks #63 and the substrate in Execution graph for passive readers: session relationships and tool-result event chronology #42.
• CLI command gating (separate follow-ups per command).

Refs

• Spun out of Add coverage and fidelity metadata to TurnRecord (#41) #76 (Coverage and fidelity metadata: distinguish missing, zero, aggregate-only, and partial usage #41 follow-up)