Add pi-session-drain Pi package

[rrvsh]

Summary

• add the pi-session-drain flake input
• include the packaged extension in Pi agent settings via its Nix package path

Validation

• nix flake show --all-systems --json
• nix eval --json .#nixosConfigurations.nemesis.config.home-manager.users.rafiq.programs.pi-coding-agent.settings.packages | grep session-drain

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Post-PR validation on nemesis:

• sudo nixos-rebuild switch --flake .#nemesis succeeded from the PR branch. New system: /nix/store/kwkgiinmj0h9jardk42qhzrhdbl4px7j-nixos-system-nemesis-26.11.20260610.9ae611a.
• pi list shows /nix/store/hkl9vqhds8lj8s16zbpjbdp1q4s8vvhb-pi-session-drain-0.1.0/lib/node_modules/pi-session-drain.
• Ran an isolated smoke test against the installed Nix package using a temporary HOME and synthetic session JSONL. Verified tool/command registration, session_drain_next, transcript omission behavior, session_drain_mark, processed filtering, and changed-session retry behavior.

[rrvsh]

Updated after status-model discussion:

• pi-session-drain now uses DB statuses only: processed and failed.
• Added session_drain_status.
• /session-drain:status is read-only aggregate status.
• Added /session-drain:drain, which marks the current active session processed before queuing the subagent drain workflow.
• Deleted stale SPEC.md; README local testing now uses git clone ... && pi -e ..
• Updated tools lock to rrvsh/pi-session-drain@cdb0d77.

Validation:

• npm run typecheck
• nix build .#pi-session-drain --print-build-logs
• sudo nixos-rebuild switch --flake .#nemesis succeeded; new system /nix/store/x2glgg8cwzfhc7j3dip18mgxrhs6clpj-nixos-system-nemesis-26.11.20260610.9ae611a
• pi list shows /nix/store/rjb328xzd3cjisf3ssrccccbzchkasy1-pi-session-drain-0.1.0/lib/node_modules/pi-session-drain
• Installed-package smoke test passed for status counts, next, transcript omissions, processed mark, changed-session requeue, failed retryable, and /session-drain:drain current-session processed behavior.

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Follow-up clarification applied:

• /session-drain:drain now only starts/queues the batch subagent drain loop.
• Added /session-drain:drain-current to mark the current active persisted session as processed.
• README updated accordingly.
• Updated tools lock to rrvsh/pi-session-drain@665ff44.

Validation:

• npm run typecheck
• nix build .#pi-session-drain --print-build-logs
• command-split smoke test verified drain does not mark current and drain-current does
• sudo nixos-rebuild switch --flake .#nemesis succeeded; new system /nix/store/m846r5gx5av4g9hqabxiszac3zqq4i70-nixos-system-nemesis-26.11.20260610.9ae611a
• installed package includes both commands at /nix/store/90dxn4y13i1rdcnl2ylxkfqba3ryygxw-pi-session-drain-0.1.0/lib/node_modules/pi-session-drain

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Follow-up fixes for test findings:

• Added a managed session-drain subagent from the extension itself. On session start the extension writes ~/.pi/agent/agents/session-drain.md only if missing or already marked managed-by: pi-session-drain; unmanaged existing files are left alone.
• /session-drain:drain prompt now tells the parent to use the session-drain subagent.
• Fixed status state write concurrency:
  • inter-process status.lock around read/append/write
  • unique temp file names using randomUUID()
  • clearer parse error for corrupted JSON state/config
• Updated tools lock to rrvsh/pi-session-drain@63bcc7f.

Validation:

• npm run typecheck
• nix build .#pi-session-drain --print-build-logs
• concurrency smoke test with parallel session_drain_mark calls preserved all records and valid JSON
• sudo nixos-rebuild switch --flake .#nemesis succeeded; new system /nix/store/qr0s2r5svwylpf5ivjvqq4d8vjx0hp9k-nixos-system-nemesis-26.11.20260610.9ae611a
• managed agent was installed and subagent({ action: "list" }) shows session-drain
• subagent tool-access smoke test: session-drain child successfully called session_drain_transcript and returned 33 entries
• installed-package concurrency smoke test passed.

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Chunked transcript drain update:

• Added session_drain_chunks for metadata-only chunk planning.
• Extended session_drain_transcript with optional until_line, plus range_complete and session_complete.
• Replaced managed session-drain with session-drain-chunk; stale managed session-drain.md is removed.
• session-drain-chunk has only session_drain_transcript and reports candidates only; parent owns synthesis/memory edits.
• Updated /session-drain:drain prompt to plan chunks, fan out chunk workers, synthesize in parent, and mark processed/failed.
• Updated tools lock to rrvsh/pi-session-drain@8b5ad5a.

Validation:

• npm run typecheck
• nix build .#pi-session-drain --print-build-logs
• chunk smoke test for 125-entry synthetic transcript: two chunks, ranged transcript returned first 100 entries with range_complete: true, session_complete: false
• sudo nixos-rebuild switch --flake .#nemesis succeeded; new system /nix/store/4vlhzg5rkd18kcilwzvx296qbvsrl4r5-nixos-system-nemesis-26.11.20260610.9ae611a
• managed agent sync installed session-drain-chunk.md and removed stale managed session-drain.md
• subagent({ action: "list" }) shows session-drain-chunk
• session-drain-chunk tool-access smoke test called session_drain_transcript for one bounded chunk and returned Outcome: chunk-processed
• installed-package chunk smoke test passed.

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Follow-up chunk/research/batch-mark update:

• session-drain-chunk now has read-only research tools: read, grep, find, ls, plus session_drain_transcript; still no edit/write/mark tools.
• Chunk agent prompt requires transcript tool as authoritative source, allows bounded local read-only research, and requires source references.
• session_drain_chunks now returns top-level session_path and session_dir.
• /session-drain:drain now tells parent to pass session path/dir and includes the synthesis checklist.
• Added session_drain_mark_many for one locked batch transaction.
• Updated tools lock to rrvsh/pi-session-drain@fa8245d.

Validation:

• npm run typecheck
• nix build .#pi-session-drain --print-build-logs
• smoke test verified chunk path/dir, managed agent tools, and session_drain_mark_many
• sudo nixos-rebuild switch --flake .#nemesis succeeded; new system /nix/store/v6a98vm0qsa1i2zr4zrrwjyh6g74nvay-nixos-system-nemesis-26.11.20260610.9ae611a
• managed installed agent now shows tools: read, grep, find, ls, session_drain_transcript
• session-drain-chunk subagent tool-access smoke test succeeded with transcript + read-only research tools
• installed-package smoke test for chunk path/dir and session_drain_mark_many passed.

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Next now returns chunks update:

• session_drain_next now treats limit as a chunk budget. Default remains 1.
• session_drain_next returns complete sessions with embedded chunks and rounds down to preserve session boundaries.
• Added optional session_id to session_drain_next for oversized-session retry.
• Oversized first session now returns no sessions plus oversized_session_id, oversized_chunk_count, and required_limit; parent prompt tells agent to retry with that session_id and required_limit.
• Kept session_drain_chunks for targeted/debug planning.
• Updated /session-drain:drain prompt to use chunks embedded in next and not call chunks in normal path.
• Updated tools lock to rrvsh/pi-session-drain@4059656.

Validation:

• npm run typecheck
• nix build .#pi-session-drain --print-build-logs
• smoke test covered chunk-budget limit, session-boundary rounding, oversized response, and session_id retry
• sudo nixos-rebuild switch --flake .#nemesis succeeded; new system /nix/store/wvz4bs1blb84si59ky7zfrai76h977rk-nixos-system-nemesis-26.11.20260610.9ae611a
• installed-package next chunk-budget smoke test passed.

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Child-session exclusion update:

• Detect nested subagent child sessions from path shape <parent-stem>/<8hex>/run-N/session.jsonl.
• Add relationship metadata on discovered child sessions: is_subagent_child, parent_session_id, parent_session_path, parent_status, run_id, child_index.
• Exclude child sessions by default from session_drain_status, session_drain_next, session_drain_chunks, and session_drain_transcript.
• Add explicit opt-in include_child_sessions: true for inspection/debugging.
• Status now reports excluded_child_sessions.
• Updated tools lock to rrvsh/pi-session-drain@1888dd7.

Validation:

• npm run typecheck
• nix build .#pi-session-drain --print-build-logs
• smoke test verified default status counts only parent sessions, reports excluded child count, next returns only parent sessions, child chunks/transcript fail by default, and explicit opt-in returns child metadata/access
• sudo nixos-rebuild switch --flake .#nemesis succeeded; new system /nix/store/sxsymnz0rjw6zw0399jn1wcc9n90gcj2-nixos-system-nemesis-26.11.20260610.9ae611a
• installed-package child-exclusion smoke test passed.

[rrvsh]

Added manual session drain service, no timer yet.

• Added Home Manager wrapper pi-session-drain-run.
• Wrapper runs pi --no-session -p <direct drain prompt>, with PI_OFFLINE=1 and PI_SKIP_VERSION_CHECK=1.
• Added user oneshot service pi-session-drain.service.
• Did not add timer yet.
• Rebuilt nemesis: /nix/store/4pdqh3naxqld6vc2frkm1q5f78m2lck8-nixos-system-nemesis-26.11.20260610.9ae611a.
• Started service with systemctl --user start --no-block pi-session-drain.service.
• Verified service is active/starting and parent session JSONL count did not increase immediately after start.
• Added follow-up todo to check results after the real drain finishes before deciding on a timer.

Commit: a382ff35 Add manual session drain service.