clankerbar-cli

README

clankerbar

Drive a coding agent through your clankerbar backlog, unattended. clankerbar respawns fresh harness sessions that work the backlog one task at a time, and survives usage limits — pausing on the cap and resuming (including on an early reset) instead of dying until you come back.

It's a local, open-source client of the clankerbar control plane: the hosted plane holds the state (your backlog, over MCP), this runs on your machine and drives your coding agent. Because it holds your credentials and can edit your code and run shell commands, the source is open so you can audit exactly what it does before you trust it with an overnight run.

Status: pre-1.0, released. The loop runs and is what drives clankerbar's own backlog; the harness adapters and the limit/budget machinery are still being hardened. It is a supported surface rather than an internal tool - see Versioning for what the v0.x line does and does not promise.

How it works

Each iteration is a fresh harness session told to work one task, landing a PR at in_review. That is the prompt knob, and the wording is exact: the served protocol reads "work the next backlog item" as one task and "work the backlog" as drain the whole ready queue in this session. One task per iteration is the default because it is what keeps a session's context bounded no matter how long the queue is, and because the operator's controls — console pause, HALT, max_iterations, the budget breaker — are consulted between iterations, so a shorter iteration is a shorter wait for them to bite. Set prompt to the drain phrase if you want the old behaviour, and expect both properties to go with it.

When a session ends, the driver spawns a new one — so context never rots across a long run, and a session killed mid-task is fine: the driver hands the task straight back to the queue (see Resilience) and the next iteration picks it up. The backlog is the durable state; the loop is thin.

On a usage limit the loop doesn't die — it pauses and polls for the reset (catching Anthropic's semi-random early resets), then continues.

Install

Download a prebuilt binary. Each release ships cross-platform binaries on the releases page - macOS and Linux, amd64 and arm64, as clankerbar_<version>_<os>_<arch>.tar.gz. Extract it and put clankerbar on your PATH. No Go toolchain required.

# macOS arm64; swap the os/arch for yours.
VERSION=0.1.0 OSARCH=darwin_arm64
curl -fsSLO "https://github.com/lecstor/clankerbar-cli/releases/download/v${VERSION}/clankerbar_${VERSION}_${OSARCH}.tar.gz"
curl -fsSLO "https://github.com/lecstor/clankerbar-cli/releases/download/v${VERSION}/checksums.txt"
shasum -a 256 --ignore-missing -c checksums.txt   # Linux: sha256sum --ignore-missing -c checksums.txt
tar -xzf "clankerbar_${VERSION}_${OSARCH}.tar.gz"
./clankerbar version

Then verify where it came from, not just that it arrived intact. The checksum above catches a corrupt or truncated download, and that is all it catches: it is served from the same release page as the archive, so anyone able to replace one could replace both. Every release is also signed with build provenance - a Sigstore attestation held by GitHub, not by the release, recording that these exact bytes came out of this repo's release.yml at a specific commit:

gh attestation verify "clankerbar_${VERSION}_${OSARCH}.tar.gz" \
  --repo lecstor/clankerbar-cli \
  --signer-workflow lecstor/clankerbar-cli/.github/workflows/release.yml

--signer-workflow is the half that makes the sentence above true: --repo alone accepts an attestation signed by any workflow in this repo, while naming the workflow pins it to the one that publishes releases. That is worth the extra line - this binary holds your credentials and runs shell commands on your machine, and provenance is the part that would notice if the archive were not ours. Needs the GitHub CLI and a gh auth login; run gh attestation verify --help for the offline and JSON-output variants.

Downloading in a browser instead of with curl gets the archive quarantined by macOS, and the binaries are not notarized, so the first run is refused with "cannot be opened because the developer cannot be verified". Clear it with xattr -d com.apple.quarantine clankerbar, or use the curl route above, which never sets the attribute.

Or build from source (requires Go 1.26+):

go install github.com/lecstor/clankerbar-cli/cmd/clankerbar@latest
# or, from a checkout:
go build -o clankerbar ./cmd/clankerbar

A source build reports the version it was stamped with - go install leaves it at the 0.0.0-dev default, so clankerbar version naming a real vX.Y.Z means you are on a release archive.

Versioning

Releases are semver tags (vX.Y.Z) and the tool is pre-1.0, so expect the v0.x line while the surface settles. Concretely, while pre-1.0:

• A breaking change can land on a minor bump (v0.1 -> v0.2). That is what the v0.x line means; pin a version if you are automating against it.
• A breaking change is never silent. Permitted is not the same as unannounced: breaking commits carry a ! (feat(cli)!: ...) and the release config hoists them into a Breaking changes heading at the top of the notes, rather than leaving them as one line among thirty.
• Releases are cut when there is something to ship, not on a schedule. The commitment is that a tag produces working, downloadable binaries.

Those promises harden at v1.0.

Usage

clankerbar run --harness=claude
clankerbar run --harness=claude --model=opus --max-iterations=10
clankerbar run --config ./clankerbar.json     # or: -c ./clankerbar.json

Flags are GNU-style: --long options, -x shorts. --config (-c) and --help (-h) are the only short aliases; everything else is long-form only. clankerbar run --help and clankerbar doctor --help list them. A short flag's value is separate (-c ./x.json) or =-joined (-c=./x.json); the inline -c./x.json form is rejected, so a typo like -cofnig cannot quietly become --config=ofnig.

If you built from a checkout before v0.1.0, this changed under you. A single dash now introduces short flags, so the Go-stdlib spelling -harness claude no longer works - use --harness claude. Anything invoking clankerbar with single-dash long options (a cron wrapper, a launchd plist, a shell alias) needs updating. The old spelling is rejected with a message naming the double-dash form rather than being quietly reinterpreted. v0.1.0 is the first release, so it ships the GNU-style spelling from the start.

Preflight: clankerbar doctor

Most of what goes wrong in an unattended run only shows up as degraded behaviour, hours in — a rejected key silently drops the loop into blind mode, a missing binary kills the first session, an unreachable plane looks exactly like an empty queue. doctor turns all of that into one cheap answer before you start:

clankerbar doctor
clankerbar doctor --config ./clankerbar.json --harness codex   # or: -c ./clankerbar.json
clankerbar doctor && clankerbar run --harness=claude   # gate a cron wrapper

It prints one PASS / WARN / FAIL line per check, with a one-line remedy under anything that isn't a PASS, and exits non-zero if any check FAILs — so it composes with && as above.

PASS  config       loaded ./clankerbar.json
                   harness: claude
                   workdir: /Users/you/dev
                   backlog: https://clankerbar.com/api/projects/acme/backlog-summary
PASS  harness      /usr/local/bin/claude (2.1.0)
WARN  config_dir   not set — the session inherits the ambient environment
                -> set config_dir (or --config-dir) so a cron/launchd run loads the same skills, plugins and auth as your terminal
WARN  backlog      https://clankerbar.com/api/projects/acme/backlog-summary — 0 claimable, 2 open question(s) — nothing to claim; the loop will idle without spawning
                -> answer the open question(s) at clankerbar.com, or expect an idle run
WARN  state_dir    /Users/you/.local/state/clankerbar/loop/dev-9f70ef211d1e0549 has a leftover STOP marker
                -> delete it, or the loop stops immediately: rm /Users/you/.local/state/clankerbar/loop/dev-9f70ef211d1e0549/STOP
WARN  workdir[acme] /Users/you/dev has no agent-instructions file (AGENTS.md / CLAUDE.md)
                -> add one here naming each repo below and where its protocol lives — a session started in a multi-repo parent loads nothing from the repos under it
PASS  permissions  /Users/you/.config/clankerbar/headless.json parses
WARN  toolchains   no grant for: go (/Users/you/dev/acme-cli)
                -> allow the verbs each one needs in /Users/you/.config/clankerbar/headless.json (e.g. Bash(go build:*), Bash(go vet:*), Bash(go test:*)) — a headless session fails closed, so an ungranted tool is refused with no prompt and its task ships unverified
PASS  budget       no ceiling configured — the loop runs until the backlog is dry or it is stopped

The checks: config (discovered, parses, validates — plus the resolved harness, workdir and derived backlog URLs), harness (binary on PATH and runnable, with its version), config_dir (resolves, exists, looks initialised for the chosen harness), backlog (creds present and the summary read succeeds — distinguishing no creds, a rejected key, a project_required key/route mismatch, and an unreachable endpoint — plus whether the queue is gated on your open questions, or paused from the console), state_dir (the driver's own directory: writable, no leftover HALT/STOP, and not sitting inside a configured workdir - a state dir under one a session is spawned in is writable by that session, which hands it the loop's own STOP/HALT switch; under a workdir nothing runs in yet it is the same trap for the next projects[] entry that inherits it), workdir (per project: it resolves, an .mcp.json reaches it, and it carries an agent-instructions file), permissions (harness-specific policy sanity), toolchains (the build tools the project's repos need are actually granted), power (whether the machine will stay awake long enough to do the work), and budget (ceilings parse and are sane).

A multi-project config gets one backlog check and one workdir check per project — one queue can be wired wrong while the others are fine. A project entry that omits workdir or mcp_config_path inherits the top-level one, and doctor resolves it exactly the way the loop does, so it never reports on a directory your sessions will not use.

The toolchains audit reads every settings file Claude merges — the --settings policy, the config dir's settings.json/settings.local.json, and each session workdir's .claude/settings.json/.claude/settings.local.json. A narrow deny (Bash(go run:*) alongside an allowed Bash(go test:*)) is reported as a hole in an otherwise-granted tool, not as a blocked one — only a bare Bash(go:*) deny means the toolchain is unusable.

Three of those exist because of failure modes that cost a real overnight run whole iterations:

• The queue said there was work and there wasn't. A ready task gated on an unanswered question still counts as claimable, so the loop spawns, the session correctly declines to pre-empt your decision, and you pay for that report ten times. Preflight now says so before the window opens.
• A session started in a multi-repo parent reads nothing. A harness loads its instruction file, skills and project settings from the session's cwd and upward — never from the repos below it. Spawn in ~/dev and every session begins by rediscovering the layout, with none of your conventions.
• An ungranted toolchain does not stop a run, it un-verifies one. A headless session fails closed, so go test that was never allowed is refused with no prompt reaching you — and the task ships written, pushed and never compiled.
• A sleeping machine does not pause a run, it freezes one. Timers use the monotonic clock, which does not advance while the machine is suspended, so a wait stops mid-flight and the loop goes silent exactly like a hang. One run lost 5h31m of a 10h window this way, waking only in 45-second Power Nap bursts.

Sleep, on laptops

clankerbar run now holds a no-idle-sleep assertion for its own lifetime (macOS; it dies with the process, so nothing outlives the run). Two caveats it cannot fix, both of which have cost a real run its night:

• A closed lid sleeps regardless. No assertion overrides clamshell sleep.
• Start the run on AC. Plugging in later does not wake a sleeping Mac, so a machine that idle-slept on battery stays down even once power arrives — its never-idle-sleep-on-AC setting never gets a chance to apply.

When a wait does get frozen, the loop now says so on the way out, rather than leaving an unexplained gap in the log:

wait of 30m0s took 2h28m11s of wall clock — the machine was suspended for ~1h58m11s;
timers are frozen while it sleeps, so an unattended run stalls silently

When the queue lies about having work

claimable > 0 means work is available, not that it can be done. A task gated on an unanswered question is claimable and unworkable: the loop spawns, the session correctly declines to pre-empt your decision, and you pay for that report every cycle. One run did it ten times.

So after three consecutive sessions that settle nothing — nothing reaching in_review or done — the loop backs that project off for 15 minutes, then 30, then an hour, capped at two. Other projects keep draining.

So does the queue simply going quiet. A poll that shows nothing to spawn for at all means the project is idle, not fruitless — there is nothing for the loop to spawn, so it has not failed at anything — and the count is forgotten along with any wait still running. Without that, parking the blocker would leave the count standing (parked is not progress a backlog can see), and the next task you file would serve out a two-hour wait it did nothing to earn.

Note "nothing to spawn for" rather than "nothing claimable": abandoned work counts as something to spawn for. A project can hold a branch whose session died, and the sweep that hands it back runs only when an agent asks the plane for its next task — so if the loop declined to spawn while the ready queue was empty, nothing would ever ask, and the branch would sit there for good. The gate is claimable + stale_claimable, both of which the queue line reports.

What bounds a recovery that never finishes is the plane, not this back-off. Taking a branch over renews its lease, so the task stops being offerable until the lease lapses again — and the poll in between reads as idle and forgets the strike. The count therefore does not climb across successive takeovers of one branch, and the local back-off will usually never reach its threshold. That is deliberate: the plane counts hand-offs per task, and once a branch has defeated its allowance it is parked and raised to you as a question instead of being offered again, which drops it out of stale_claimable for good. So the spend is bounded per branch by the plane, at a session or so per lease period, rather than by three strikes here. The local back-off still bites the case it was built for — a target that keeps being offered the same unfinishable work without the lease resetting.

Three rather than one, because a genuinely large task can span several sessions before anything reaches a reviewer, and backing off then would throttle exactly the deep work the loop exists to do.

Answering the question ends the wait, and so does any other progress: you merging a PR, another machine's loop settling something. Both are seen on the next poll, so "immediately" means within one idle_poll_interval (60s by default), not sooner. The answer is the one worth spelling out, because it is what the back-off message asks you to go and do: an answer moves neither in_review nor done, so a falling open-question count is the only trace of it the loop can see, and it watches both signals for that reason. Answer while a session happens to be running and the loop gives that project one immediate retry rather than the next rung of the ladder. That session still settled nothing, and its strike stands.

WARN vs FAIL is the "would this still make progress?" line: no creds and an unreachable plane WARN, because the loop drains blind and still gets work done; a rejected key and a key/route mismatch FAIL, because they never self-heal and every session the loop spawns carries the same broken credential.

Control an in-flight run with markers in the state dir, which lives OUTSIDE the workdir - $XDG_STATE_HOME/clankerbar/loop/<workdir-slug>, i.e. ~/.local/state/clankerbar/loop/<workdir-slug> by default. doctor prints the resolved path:

touch ~/.local/state/clankerbar/loop/dev-9f70ef211d1e0549/STOP   # stop gracefully (responsive even mid-wait)

An explicit state_dir wins, but pointing it back inside a workdir gives every session spawned there the ability to write these markers. doctor WARNs whenever the resolved state dir sits inside a configured workdir - including the default, if your workdir happens to contain ~/.local/state.

You can also pause a run remotely from the clankerbar web console (Settings → Pause) — per project. A paused project stops getting new sessions (other projects keep draining) and the loop idle-polls until you Resume — without exiting, and without killing an in-flight session (a pause is honoured between iterations, like STOP). Remote pause rides on the driver's cheap backlog read, so it needs a wired poller: a CLANKERBAR_API_KEY and a resolvable plane URL. Your account key (mint at clankerbar.com/account/api-keys) is the normal choice — the driver polls the project-in-path summary route whenever it knows the slug, which it derives from your .mcp.json's /mcp/<slug> URL or from the projects config (below). A project-scoped key works too (the CI-style setup). With no creds or no resolvable endpoint the loop drains blind and can't see the flag — the local STOP/HALT markers remain the fallback there. Two misconfigurations hard-stop (non-zero exit) instead of blind-draining doomed sessions: a revoked/wrong key (401/403), and an account key with no derivable project slug (400 project_required from the legacy slug-less route) — give the loop a slug via projects or an /mcp/<slug> .mcp.json.

Visibility

The driver logs milestones to your terminal as it goes (timestamped): spawning, queue state each poll, done + tokens/cost, usage-limit pauses, transient retries. The Claude harness runs with --output-format stream-json, so the agent's own progress — assistant text and → Tool markers — streams live too, and each attempt is captured to its own <state-dir>/iteration-<ts>.log.

Checking what a session says it delivered

The control plane holds the backlog and takes a clanker at its word. When a session records a branch (update_task(branch: …)) or declares a delivery merged (delivery.commit + integrationBranch), nothing on the plane can look at a repository to see whether either is true. One task read done for four days while about 900 lines of its work sat unpushed on one laptop, and its own PR merged a stale snapshot.

The driver is already local and already in the git tree, so it checks both claims after each session — no new credentials, no plane change:

• A recorded branch is really on the remote, and the local tip is an ancestor of the remote tip. A local branch ahead of its remote is the failure above.
• A declared delivery really landed: commit is an ancestor of the remote tip of integrationBranch — the same ancestor check the plane asks the clanker to attest to, run rather than trusted. The integration branch is read from the remote, never from a local main that is routinely tens of commits stale. Only a closure is checked this way: a hand-off to in_review carries the delivery it is proposing, and at that moment nothing has merged yet. And only a commit id counts — a revision expression like main or HEAD is trivially its own ancestor, so it is reported as unverifiable rather than checked.

DELIVERY UNVERIFIED — CLA-134: branch "clanker/x" is ahead of origin/clanker/x by
12 commits — local tip 4a91c0de, remote 0b3f21aa; that work is UNPUSHED and
exists only in /Users/you/dev/acme

It warns; it does not refuse. A failed check is logged loudly and names what is unpushed or unmerged, but the session's own report stands — the driver does not revert a status a session chose on the strength of a check that could be looking at the wrong tree. When the merge check ran, its verdict is written back to the task as delivery.mergeVerified, true or false, so the answer outlives the log.

It fails open. No git, no remote, a workdir that is not a repository, a remote tip that cannot be fetched — all report could not verify and the run carries on. Blocking a legitimate closure because the tree could not be found would be worse than the gap this closes. A check that could not run never writes an attestation: not knowing is not the same as knowing it is fine.

Finding the tree. The driver spawns sessions in a workdir, but the work happens in a per-task worktree it did not create — and the workdir is routinely a multi-repo parent (~/dev) that is not a repository at all. Linked worktrees share their repository's refs, so the specific directory does not matter: the driver looks for the repository whose refs carry the branch, searching the workdir and its first two directory levels (enough to reach both ~/dev/<repo> and ~/dev/<repo>-wt/<task>). Repositories are never descended into and bare ones are skipped, so the search costs a bounded handful of git rev-parse calls. If two repositories under the workdir carry the same branch — a review clone sitting beside the session's own tree — that is reported as unverifiable too: checking the wrong tree is worse than not checking.

This covers unattended runs only, by design: an interactive session bypasses the driver entirely.

Rescuing work a killed session left behind

A usage limit kills a session mid-turn. There is no graceful shutdown, so the protocol's commit, push, record the branch before you let go never runs — there is no before. The uncommitted work survives in the worktree and nowhere else: invisible to the plane, invisible to another machine, invisible to the next session. The lease then expires with no branch recorded, the task correctly returns to ready, and the next clanker starts from nothing — redoing hours of work sitting intact on the same disk. One such task cost 112.7M tokens, a third of a day's spend, for work that was done twice.

So when a session ends still holding a task, the driver looks for the worktree it was working in and, if anything is uncommitted, commits it, pushes it, and records the branch on the task — turning a redo into a takeover:

salvaged CLA-314: committed the uncommitted work in /Users/you/dev/acme-wt/cc561415
as 4a91c0de and pushed it to origin/clanker/cc561415-a-session-killed-mid-task
recorded clanker/cc561415-a-session-killed-mid-task as the hand-off branch for
CLA-314 — the next clanker takes it over instead of starting again

On every abrupt ending, not only a usage limit. A crash, a killed process and a limit are different to the supervisor and identical to the worktree, and the limit is only detected by parsing a stream that may not have arrived whole. Running it when it was not needed costs nothing: a clean worktree commits nothing, pushes nothing, and records nothing — an empty hand-off would send the next clanker to fetch a branch with nothing on it, which is worse than recording none at all.

It commits work it cannot vouch for, and says so. The driver cannot tell a half-applied refactor from good work, and the failure it exists to prevent is caused by dropping work, never by keeping it. So the commit lands with a subject that reads WIP salvage: … (unreviewed, may not build) and a body saying in as many words that nothing here was reviewed, built or tested. It skips hooks and commit signing on purpose: a lint hook would reject exactly the half-finished tree this exists to save, and a signing passphrase has nobody to ask at 3am. One exception: a worktree holding an unresolved conflict is left exactly as it is, because committing it would record a state nobody chose — it would fabricate a resolution out of the conflict markers and push a file that reads as source with <<<<<<< in it. That covers both a git operation still in flight (a merge, rebase, cherry-pick or revert) and a conflict nothing is holding open: a git stash pop, git apply --3way or git checkout -m leaves unmerged entries with no state file at all, so the unmerged index is checked as well as the operation. Either way it is logged as STRANDED WORK LEFT AS IS with the path.

It cannot touch a tree that is not this task's. The worktree is identified by its checked-out branch carrying clanker/<first 8 characters of the task id> — the task-id half, not the title-derived slug, so a task retitled mid-flight is still matched. A detached HEAD is never matched, main and staging can never match, and two trees answering to the same task is reported rather than guessed at. Nothing is ever forced: no push --force, no checkout, no branch creation, no worktree removal. A push the remote rejects leaves the commit safely on this machine and records no branch — a recorded branch is a promise that another machine can fetch it.

Recording a branch is not settling a claim. The record carries no status, so it cannot move a task, clear a holder, or post ready over work already in review — which is why it is still safe on a session whose output could not be read whole, where handing the claim back is forbidden. Once a branch is recorded, the claim is deliberately not handed back either: the lease expires and the task stays a takeover, so the next clanker is told there is work to fetch.

Skills, plugins, and auth

A headless session loads project skills from the working directory (.claude/skills/) and user/plugin skills + auth from the config dir. Set config_dir (→ CLAUDE_CONFIG_DIR / CODEX_HOME) so an unattended run loads the same skills, plugins, and login as your interactive session — a bare cron environment would otherwise have none of them.

Config

Flags override the config file, which overrides defaults. Default file locations: ./clankerbar.json, then ~/.config/clankerbar/config.json. (JSON today; TOML is the likely final format.)

{
  "harness": "claude",
  "model": "opus",
  "prompt": "Work the next backlog item.",
  "mcp_config_path": "./.mcp.json",
  "config_dir": "~/.claude",
  "idle_poll_interval": "60s",
  "poll_interval": "30m",
  "max_retries": 0,
  "retry_cap": "5m",
  "budget": {
    "max_tokens": 0,
    "max_cost_usd": 0,
    "max_wall_clock": "6h"
  }
}

mcp_config_path defaults to <workdir>/.mcp.json when that file exists — Claude's headless mode does not auto-discover it, so under harness: "claude" the default is what gives spawned sessions their clankerbar tools. It always gives the driver a project slug to poll with, whichever harness is configured.

The other two harnesses do not read that file, and one of them chokes on it. The default is applied regardless of harness, so this matters the moment you switch:

harness	what it does with mcp_config_path
claude	passed as --mcp-config (with --strict-mcp-config) and read as Claude's .mcp.json.
codex	ignored. codex has no per-run MCP flag; its servers come from [mcp_servers] in config.toml under CODEX_HOME (which config_dir pins).
opencode	passed as OPENCODE_CONFIG, and must be an opencode config - servers under mcp, not Claude's mcpServers. Pointed at a Claude-shaped .mcp.json, opencode refuses to start and every session dies at spawn.

Under opencode, set mcp_config_path explicitly to an opencode config. Leaving it out does not opt out: an empty value re-runs the <workdir>/.mcp.json discovery, so a workdir that carries a Claude .mcp.json hands it over no matter what. Run clankerbar doctor - it prints the caveat instead of a verdict where the file is not read, and FAILs the workdir check when opencode is pointed at a Claude-shaped one.

Point it at your workdir, not at a checkout of this repo. The .mcp.json at the root here is the maintainers' own agent wiring and names the clankerbar project slug; running the loop from inside this checkout would have it poll a queue you cannot read, which it refuses rather than drains.

Multi-project: one instance, many queues

One loop instance can drive several projects with a single account-scoped key — you never need an instance per project, or per-project keys. Declare the projects; the driver polls each queue and round-robins sessions across whichever have claimable work, each session spawning in its own project's workdir (whose .mcp.json names /mcp/<slug>, selecting that project's tools):

{
  "harness": "claude",
  "projects": [
    { "slug": "clankerbar", "workdir": "~/dev" },
    { "slug": "ezyapp", "workdir": "~/work/ezyapp" }
  ]
}

Per entry: slug (required, the <slug> in /mcp/<slug>), workdir, and optionally mcp_config_path (defaults to <workdir>/.mcp.json). Budgets, max_iterations, and the STOP/HALT markers stay instance-global — one operator, one spend pool; the console pause is per project. With no projects list, the top-level fields drive a single project exactly as before.

Resilience

A fresh session can die on a server blip (API 5xx / overloaded) or a network hiccup — nothing to do with the task. These are retried with exponential backoff (30s → 60s → … capped at retry_cap), re-running the same iteration; a fresh session reclaims any half-done task, so a retry costs minutes, not work. Detection is anchored (Claude's API Error: prefix, connection-error strings), so a task log that merely mentions an HTTP 500 isn't mistaken for a dead session, and a 400 still stops. max_retries: 0 (the default) means never give up — keep retrying at the ceiling until the API recovers, right for a daemon; set a positive number to bound it. A usage-limit pause and a transient retry both re-run the same iteration and neither advances the iteration count. STOP stays responsive during any wait.

What gets read as a failure. A session's output is the whole event stream, and the events quote the backlog verbatim — the task the session claimed is sitting in the same bytes. So both classifications read only what the harness said: its stderr, its own non-event output, its typed error events, and Claude's terminal_reason. A task whose body happens to say "hit your", "usage limit" or "api error: 500" is narration, and narration is never a cap and never a blip.

Handing the task back. A claim carries a 30-minute lease that the session heartbeats. When a session ends mid-task, that lease is left ticking with nobody renewing it — and clankerbar charges the task a reclaim to sweep it up, of which there are only two before the task is parked for a human. So the driver watches the session's stream for what it claimed, and hands the task straight back (update_task(status: ready)) on every exit: usage limit, transient blip, outright failure, or a clean finish with the work unfinished. The usage-limit case is why this matters most — the pause that follows can be hours, and the release is ordered before it.

One case is deliberately left to expire: a task whose session pushed a branch. clankerbar computes its takeover hint only for an in-progress task with a dead lease, so handing that one back would discard the very flag telling the next clanker there is work to pick up. There it takes the reclaim and keeps the hand-off. Releasing is best-effort throughout — if the plane refuses or is unreachable, the loop logs it and carries on, since an expiring lease is merely the behaviour it already had.

Not getting locked out

No coding-agent harness lets a headless caller read its remaining subscription quota, so clankerbar cannot stop at a precise "80% of the window". Two reliable alternatives, in order of preference:

1. Separate credentials — run the loop under a different account / API key than your interactive agent use, so it physically cannot spend your daytime quota. This is the only can't-be-wrong option.

2. Budget circuit breaker — set budget.max_tokens / max_cost_usd / max_wall_clock; the loop self-accounts and stops early. Blunt but simple — tune it by watching a couple of runs.

   Prefer max_cost_usd. It comes straight from the harness's own total_cost_usd, so it measures the thing you actually care about. max_wall_clock counts the hours a run spends waiting out a usage limit, in which almost nothing is billed — one run elapsed 10h23m against an 8h ceiling with 5h31m of that asleep. Keep it as an outer bound on how late a run may finish, not as your spend ceiling. doctor warns if it is your only dial.

   max_tokens counts about ten times more than it used to. Token totals now include cache reads and writes, which input_tokens excludes and which dominate a long agentic session — one run reported 140,387 tokens against $147.98 of real spend, about $1.05 per thousand, which is no model's price. The old number was the wrong one, but a max_tokens you tuned against it will now trip roughly ten times sooner. Re-tune it, or move to max_cost_usd.

   max_wall_clock is measured on the monotonic clock, so time the machine spends suspended does not count against it. That is also the clock the limit-reset check uses, so the two cannot disagree about how much of a run is left.

   When a limit's stated reset falls beyond max_wall_clock, the loop stops right then and tells you when the quota returns, rather than sleeping through the window to run one session against the fresh quota and stop on the next check.

   Every ceiling is also checked inside an iteration, before each re-run of a session that paused on a usage limit or backed off on a transient blip. Those waits can repeat for hours, and a run that reached its ceiling during one stops there instead of spending another session first.

   The polls during a pause count too. Waiting out a usage limit means probing for an early reset every poll_interval, and a probe is a real harness session — cheap (a one-character prompt, with the harness locked down to no tools or read-only), but not free, and a week-long cap polled every 30 minutes is a few hundred of them. Their tokens and cost go into the same running total the breaker reads, so a pause whose probes alone cross a ceiling ends on that ceiling rather than polling on.

   A session whose spend cannot be measured stops the run, if you set a spend ceiling. Every figure the breaker reads is parsed out of the harness's event stream, and one enormous line — a tool_result carrying a large file read — can end that stream early. The session's own total arrives in its last event, so a stream cut short reports near-zero for a session that may have cost hundreds of dollars. The loop refuses to count that figure, says so loudly, and then stops if max_tokens or max_cost_usd is set, because the ceiling you asked for can no longer be honoured. Under max_wall_clock alone, or with no ceiling at all, it carries on: the clock does not depend on anything the child said. The same session's task is left to its lease rather than handed back — the settle that released it may be in the bytes that never arrived.

Harnesses

Harness	Status
Claude Code (claude)	primary
Codex (codex)	adapter present; parsing being hardened

New harnesses are a small adapter (internal/harness). Contributions welcome.

License

MIT (see LICENSE).