fix(session-manager): let agents find and read archived sessions

[richard-fairthorne]

Fixes #7125

What changed

Agents lost access to knowledge the moment a user archived a session: session_search silently skipped archived sessions (no opt-in existed) and session_list could not show them. This PR makes archived history discoverable again, following the approach recommended in the issue thread:

• session_search includes archived sessions by default (opt-out via include_archived: false). Search is a discovery operation; the caller is rarely the same agent that archived the session, so a default-off flag would not fix the failure mode.
• Active-first scan ordering. SDK sessions are partitioned by time.archived; archived ids are appended after active ids. Within the existing MAX_SESSIONS_TO_SCAN budget, archived sessions can never displace active ones, and every result findable before this change remains findable (strict superset).
• session_list keeps its default (archived hidden, sidebar semantics) and gains include_archived: true to include them.
• [archived] provenance marker on hits and rows, so the calling agent knows restore semantics may apply.
• No changes to session_read / session_info (read path already fixed via the messages probe).

Implementation notes: getSdkAllSessions() now returns { active, archived } partitioned client-side; the stable SDK Session type does not declare time.archived yet (wire field), so the read is defensive. On servers that do filter archived sessions from GET /session, archived ids simply stay absent and behavior degrades gracefully to the pre-fix state.

Observed behavior (live QA)

Driven on real opencode 1.18.15 in an isolated XDG sandbox (HOME + XDG_* redirected, sandbox DB seeded with one active + one archived session containing a unique needle; archived session deliberately given the newer time_updated to stress ordering):

Call	Result
session_search({query: needle})	Both sessions found; archived hit rendered [ses_qa_archived] [archived] ...; active hit listed before archived despite older time_updated
session_list({include_archived: true})	Both rows, archived row marked [archived], active first
session_list({})	Only the active session (unchanged default)

Also verified against the server: GET /session on 1.18.15 returns archived sessions with time.archived set, so the client-side partition works on the current release line. Full evidence (transcripts, isolation proof) in .omo/evidence/2026-08-22-session-search-archived/EVIDENCE.md.

Verification

• bun test packages/omo-opencode/src/tools/session-manager/ — 74/74 pass (incl. new tests: search default-on, explicit opt-out, list default-off/opt-in, active-first append order, legacy sessions without time.archived treated as active, marker propagation, result-limit behavior)
• tsgo --noEmit -p packages/omo-opencode/tsconfig.json — clean
• Root-suite and full typecheck:packages cannot fully run in a fresh worktree (senpi/codex vendored artifacts are install-generated, not git-tracked); the failing tests there fail identically on clean dev in this environment and pass in a fully installed checkout. Not touched by this diff.
• Live-surface QA per repo protocol (see Evidence above).

Residual risk

• MAX_SESSIONS_TO_SCAN still bounds the scan (by design, unchanged); archived sessions consume the remaining budget after actives.
• Behavior on servers that filter /session degrades to pre-fix (never worse).

---

Summary by cubic

Restore archived session discoverability for agents. Previously, session_search silently skipped archived sessions and session_list could not show them; now search includes archived by default (opt-out), and lists can include them with a flag, with clear [archived] markers.

• Reviewer notes:
  • Active-first scan ordering: SDK sessions are partitioned by time.archived; archived IDs append after active IDs within MAX_SESSIONS_TO_SCAN, so archived never displace active.
  • session_search: new arg include_archived (default true). Matches from archived sessions are marked [archived].
  • session_list: default unchanged (archived hidden). New arg include_archived: true to include them; rows from archived sessions are marked [archived].
  • Storage API adjustments: SDK getSdkAllSessions() returns { active, archived }; getAllSessions() returns { ids, archivedIds }. Callers updated; file-backed fallback unchanged.
  • Compatibility: if servers omit archived sessions from GET /session, behavior degrades to pre-fix. Extensive tests cover defaults, opt-in/out, ordering, and marker propagation.

^{Written for commit 3495e08. Summary will update on new commits.}

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