astern

crowsnest watches the sessions running right now; astern looks back at the wake they left — the transcripts Claude Code already keeps under ~/.claude/projects/. It mines them for what problems recur, where agents get stuck, what one-off code keeps being rewritten, and which words you and your agents don't share, without spending a token twice.

Start here

pip install astern

astern sync                        # read new or changed transcripts, run the free (heuristic) lenses
astern sessions                    # what's synced, newest first
astern show <sid-prefix>           # one session: meta, ledger state, last turns, findings
astern why <file>:<line>           # which session turn wrote this line (see below)
astern report friction             # (in progress) a lens's findings as a markdown report
astern judge                       # (in progress) run the LLM-judged lenses over what's synced
astern estimate                    # (in progress) token/cost estimate before a judge batch runs

pip install "astern[recall]"       # + ir, for searching what past sessions already know
astern index                       # index the store into ir corpora (idempotent)
astern recall "what did we decide about the ledger"    # ...and ask it
astern install-skills              # link the shipped skills into ~/.claude/skills

sync, sessions, show and why are shipped today. report, judge and estimate are being built out by other agents against the same store and ledger; once they land, the one-command loop is astern sync && astern judge && astern report friction.

What it extracts

Each lens asks one question of a session and returns typed, evidence-backed findings — every finding points back at the turn it came from. Method: H = deterministic heuristic, zero tokens; L = LLM-judged, spends subscription tokens via the local claude CLI; H→L = a heuristic shortlist that only the survivors get judged on.

Session handoffs (Q) are deliberately not a lens here — that's openloops, linked rather than re-derived. The full catalogue, with the signal each lens reads and the sink it feeds, is plan §2 (see "The seams" below).

Recall — what past sessions already know

astern recall "<query>" answers what did we already think, try and decide about X without re-reading a transcript. astern is only the record source here: ir owns the indexing and the search, and the multi-hop search loop belongs to raglab. Install the extra (pip install "astern[recall]"), run astern index after a sync, and ask.

Two grains, indexed as two ir corpora because they answer different questions:

Unfiltered, a recall also reaches the skills and reports corpora when this machine has them (weighted below the sessions, so they inform rather than crowd out). --project X and --since-days N are hard metadata filters; a project is resolved through the store into its session ids, because a session about a project often runs from a group dir or a worktree whose name says nothing about it.

Embedding is local and offline: ir's all-MiniLM-L6-v2 by default — no API key, no per-query cost — with --embedder light (numpy-only hashing) for a build with no model download. Each hit carries a pointer, the astern show command that fetches the full record: a hit is an address, not an answer. The shipped astern-recall skill drives the whole loop, ending in a briefing written to the repo the question was about.

episodes — a third grain, consecutive turns on one topic — is deliberately not built yet (issue #7).

Never spending a token twice

Every lens run goes through the ledger: one entry per session, keyed on the transcript file's fingerprint (size + mtime) and, per lens, its version and the last turn index it has seen. From that, ledger.plan() picks one of three actions:

• skip — this lens version already covered every turn that exists in the transcript.
• incremental — the session grew (it was resumed); only lenses that declare incremental=True get handed just the new turns (from_index onward) plus their own prior findings, and extend rather than redo.
• full — never analyzed, or analyzed by an older lens version; everything is reprocessed.

A heuristic lens (kind='H') costs nothing, so paying for full on every source change is fine. The ledger earns its keep on the LLM lenses (kind='L'): a resumed session must not pay again for turns it already paid for, and astern sync never re-reads a transcript whose size and mtime it already has on file.

Tracing a line back to the session

astern sync --kinds session,subagent            # why needs the subagent transcripts
astern why astern/judge.py:115                  # a line
astern why 589f17a --commit                     # or a whole commit

astern why answers which session turn wrote this line, after the fact, from transcripts you already have. The chain has three links, and each one exists because the link before it is not enough:

1. git. git blame -L names the last commit to touch the line — which, after a CI ruff format pass, is the bot. git log -S names the commit whose diff first contained the text. Both are reported; when they differ, the second is the one you wanted.
2. The commit trailer. Claude-Session: https://claude.ai/code/session_<id> names the claude.ai session, which is not the local transcript's sessionId. The join lives in the transcript itself, as a bridge-session record ({"sessionId": "<uuid>", "bridgeSessionId": "cse_<id>"}), which astern sync keeps as bridge_session_id. (The live registry under ~/.claude/sessions/<pid>.json carries the same pair, but dies with the process, so it cannot answer about last month.)
3. The store. The session's turns and its subagents' are searched for the Edit / Write / Bash call whose input contains the line, whitespace-normalized first and then with quotes and integers flattened, so a reformatted line is still found. Each hit reports session, subagent, turn index, the prompt that led to it, and the assistant's prose around it.

The subagent half is not a refinement — it is usually the whole answer. A session that delegates never has the code in its own turns, so sync must have been run with --kinds session,subagent; why says so in notes when it wasn't. That is not the default because on a real corpus (290 sessions, 4547 nested transcripts) it is 50.7 s and a 330 MB store against 7.6 s and 87 MB for sessions alone.

With no trailer (older work, another machine, another account) step 2 has nothing to say and step 3 runs over every session whose cwd is inside the repo, inside a date window around the commit. If that still finds nothing, the usual reason is the other home: pass --home ~/.claude-iq to sync, because a second account's transcripts are a different corpus.

astern and Entire

Entire CLI (MIT) answers the same question from the other end: it hooks into Claude Code as the work happens and writes a checkpoint — transcript, prompt, token usage, file attribution — into a git ref, so entire why file:line is exact and travels with the repo. astern is the retroactive reader for everything Entire did not record: work done before it was enabled, in repos where it never was, and on the second account. When entire is installed and the repo is enabled, astern why runs it first and includes its answer verbatim under entire; astern's own chain runs regardless.

Two rules if you adopt it:

• Entire's refs are never pushed. Checkpoints hold the verbatim transcript, and its redaction is best-effort for secrets and does nothing at all about absolute paths — the cwd of every record is in there. Entire pushes them by default: it installs a pre-push hook that pushes refs/entire/checkpoints/* to the elected remote alongside your own push (no remote.*.push refspec is involved, so git config --get-all remote.origin.push shows nothing and git push --dry-run is silent about it). Turn it off per repo with entire configure --skip-push-sessions, which writes strategy_options.push_sessions: false into .entire/settings.json.
• The Claude Code hook is per repo, and the user's own call. entire agent add claude-code writes eight hooks into the repository's .claude/settings.json and leaves ~/.claude/settings.json alone. There is no global install; enabling it for every repo is a decision to make once, deliberately, not a side effect.

Where things live

The store is dol-backed JSON files under ~/.local/share/astern/ (sessions, turns, findings, ledger, judgments) — override with $ASTERN_DATA_DIR to keep an experiment out of the real store. The transcripts it reads come from ~/.claude by default — override with $ASTERN_HOME to point at a second account or a synced copy of another machine's home. Both are seams: any MutableMapping serves as a store, and homes() takes a single dir, an iterable of dirs, or None.

The seams

Five things in astern are deliberately swappable, each with a strong out-of-the-box default and a named replacement:

What's deliberately not a seam: the lens registry (a module-level dict), report templates, the finding dict shape, and the openloops.egress scrub step on every sink — none of these are meant to vary.

Not in astern

• Live sessions — that's crowsnest's axis (this minute), not astern's (the wake).
• Obligation tracking — what's owed, blocked, or open — that's openloops.
• Transcript viewers, full-text search, cost dashboards — claude-code-log, cc-transcript, episodic-memory and ccusage already do these well; install them alongside astern rather than rebuilding them here.
• Writing into CLAUDE.md, skills, or memory. Every lens emits candidates — mined skill/rule/function/memory suggestions — for a human to accept through skill, opsward, coact, or ge.memory. Nothing here writes automatically; that's the same "report, never repair" invariant priv upkeep carries.

Development

pip install -e ".[dev]"
pytest -q                            # the test suite
pytest --doctest-modules astern      # every module's own doctest