agent-session-kit 0.6.0

Every session can now say how full its context window is — measured where
the harness records it (Codex, Grok Build), derived from usage where it
does not (Claude Code) — plus Codex's rate limits as a quota, and a
compaction count. eventSchemaVersion is 3: hosts re-seed stored snapshots.

Added

• Per-session context-window usage — the /context gauge.
  SessionSnapshot.contextUsage is a ContextUsage: used, window,
  cached, the timestamp it was read at, and whether the window was
  measured or derived. One definition of used across every harness —
  the tokens that were in the model's context when it was last called, cached
  prefix included, the reply just generated excluded, because that lands in
  the next call's input. Folded by SessionStateReducer from a new
  AgentEventKind.contextUsage(used:window:cached:source:), which is a
  level and never summed; usage remains the delta it always was. A reading
  stamped before the one on record is dropped, so a gauge cannot flicker
  backwards when a file-mtime-stamped reading is merged behind a log line.
• SessionSnapshot.compactions, folded from AgentEventKind.compaction.
  One compaction is normal; four in an afternoon is the shape of a session
  that keeps forgetting what it was told. A compaction does not zero
  contextUsage — the window really did empty, but by how much is not on
  disk, and the next model call says so within a step.
• ModelContextWindows, the model-id → window lookup for the stores that
  record the token counts but not the size of the window they filled. Prefixes,
  a marker rule for the long-context variants (claude-…[1m]), a documented
  default of 200,000 for the Claude family, and nil — not a plausible guess —
  for a model nothing matches. Hosts pass their own with
  ModelContextWindows.standard.overriding(…), accepted by ClaudeLiveAdapter
  and ClaudeCoworkLiveAdapter.
• SessionSnapshot.quota and AgentEventKind.quota(usedPercent:resetsAt:plan:),
  from Codex's rate_limits. Read off the rollout; nothing here asks a network
  what a limit is. Only the primary window becomes an event — a row with two
  percentages and no room to label them is worse than one showing the limit a
  person is about to hit — and resets_in_seconds, which older rollouts write
  instead of resets_at, is resolved against the record's clock so a
  replayed rollout does not claim its limits reset an hour from now.
• GrokSignalsReader, which turns signals.json's contextTokensUsed and
  contextWindowTokens into a measured reading. Not a tailer: the file is
  rewritten in place, so there is no cursor to advance and no history to
  replay. It stats on every poll and parses only when the stamp moved, and
  rides along inside GrokSessionTailer rather than earning a watch of its
  own — signals.json stays out of mightBeSessionFile and out of the
  source's auxiliary paths, because Grok rewrites it many times a minute and a
  host waking on each rewrite is the storm that rule exists to prevent.
• CodexJSON.double, for the fractional percentages Codex writes.

Changed

• AgentSessionLive.eventSchemaVersion is 3. Two cases were added to
  AgentEventKind and three fields to SessionSnapshot, both of which are
  encoded structurally, so a host that persisted rows re-seeds rather than
  decoding a model it no longer speaks.