fix(session): refuse foreign format versions before parsing current structure
Review round: the JSONL backend now refuses a foreign header version straight from the raw header line, before validating today's header shape or decoding any event row, so a structurally different future format reports the upgrade direction instead of corruption (shared message builder sessionFormatVersionRefusal). HMR live-prefix adoption runs the unknown-type guard like the other read paths. The appendCore comment now states why the unknown-type guard is read-side only, the loadStoredFrom JSDoc and README pin the seek-vs-sequential refusal-scope divergence, and the generated catalog preamble lists the ignorable envelope field.
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@@ -89,7 +89,7 @@ interface SessionHeader {
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## Format refusal — logs a build cannot faithfully read
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A backend refuses a log it cannot faithfully interpret with `SessionFormatUnsupportedError`, distinct from `SessionPersistenceCorruptionError` because nothing is damaged. A header `version` ahead of `SESSION_FORMAT_VERSION` names the direction ("written by a newer harness — upgrade the harness to open it"); one behind it states that this build ships no upgrade path. After legacy-shape normalization, an event type outside this build's generated vocabulary (`KNOWN_SESSION_EVENT_TYPES`, emitted by `gen-persistence-catalog`) refuses the same way unless the event's envelope carries `ignorable: true` — silently skipping an unrecognized required event could change how the rest of the log must be read. The message appends the raw log path when the backend keeps one artifact per session, so the refused text stays reachable. Design rationale and the deferred upgrader chain live in the [session-log-version-mechanism note](../../.agents/notes/implemented/architecture/2026-08-10-session-log-version-mechanism.md).
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A backend refuses a log it cannot faithfully interpret with `SessionFormatUnsupportedError`, distinct from `SessionPersistenceCorruptionError` because nothing is damaged. A header `version` ahead of `SESSION_FORMAT_VERSION` names the direction ("written by a newer harness — upgrade the harness to open it"); one behind it states that this build ships no upgrade path. After legacy-shape normalization, an event type outside this build's generated vocabulary (`KNOWN_SESSION_EVENT_TYPES`, emitted by `gen-persistence-catalog`) refuses the same way unless the event's envelope carries `ignorable: true` — silently skipping an unrecognized required event could change how the rest of the log must be read. The message appends the raw log path when the backend keeps one artifact per session, so the refused text stays reachable. The JSONL backend refuses a foreign version straight from the raw header line, before validating today's header shape or decoding any event row — a structurally different future format still reports the upgrade direction, never "corrupt"; SQLite gates whole-file structure through its own `SCHEMA_VERSION` pragma first. Design rationale and the deferred upgrader chain live in the [session-log-version-mechanism note](../../.agents/notes/implemented/architecture/2026-08-10-session-log-version-mechanism.md).
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## `CreateSessionOptions` — seeding and metadata
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@@ -346,5 +346,5 @@ abstract listSnapshots(signal?: AbortSignal): Promise<SessionPersistenceSnapshot
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Types: [SessionEvent](session.md) · [SessionId](core.md)
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Source: [`packages/session/session-persistence/src/index.ts:73`](../../packages/session/session-persistence/src/index.ts)
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Source: [`packages/session/session-persistence/src/index.ts:74`](../../packages/session/session-persistence/src/index.ts)
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<!-- END GENERATED cordis-surface -->
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