# Contributing to cctop
Thanks for helping improve cctop. Please keep changes focused and include tests
when behaviour changes.
## Development
Build and run the test suite with Rust 1.89 or newer (the code uses let-chains and std's file locks):
```bash
cargo test
cargo clippy --all-targets
```
Before opening a pull request, run the whole gate. CI sets
`RUSTFLAGS: -D warnings`, so clippy output that looks advisory locally is a
build failure there:
```bash
# -D warnings is set in .cargo/config.toml
cargo fmt --all --check
cargo clippy --all-targets
cargo test
cargo publish --dry-run --workspace --allow-dirty # what `verify / package` runs
```
### A build cache that works across worktrees: kache
Agents each work in a worktree of their own, with a `target/` of their own,
so without a shared cache every one of them starts by compiling all ~540
crates. [kache](https://github.com/kunobi-ninja/kache) is the `rustc` wrapper
that shares them, locally as it does in CI (`kache-action` in
`.github/workflows/verify.yml`):
```bash
# a release binary from github.com/kunobi-ninja/kache/releases, or:
cargo install kache --locked
kache init --no-shell --no-service # writes rustc-wrapper = "kache" to ~/.cargo/config.toml
kache doctor
```
It is set in the user-level `~/.cargo/config.toml`, never in this repository's
`.cargo/config.toml`: there it would break the build for anyone without kache
installed. `kache stats --last-build --root <checkout>` says what one build
restored, and `kache explain <crate>` why a crate missed.
**Why not sccache**, which this machine used before: its Rust cache key hashes
the compile's command line raw, and that line carries the target directory
(`--out-dir`, `-L dependency=…/target/debug/deps`, the `--extern` paths). A
worktree's `target/` is at another path, so nothing one worktree compiled ever
matched in the next — the same `memchr` built twice under two `CARGO_TARGET_DIR`s
is a miss, under the same one a hit, whichever worktree runs it. sccache's
`basedirs` rewrites C/C++ paths only, not Rust's. kache replaces the workspace,
target and home directories with placeholders before hashing, so a second
worktree restores the first one's output.
Measured on 2026-10-09 (6 cores, load 5 to 12 from another agent building at
the same time), `cargo test --no-run` on the same commit:
| first worktree, empty kache store | 211 s | 0 of 544 crates |
| second, fresh worktree | 79 s | 426 of 434 crates |
What still compiles in a second worktree is cctop's own: `cctop-core`'s build
script reruns for a new checkout on purpose (see `CCTOP_CHECKOUT` in
`crates/core/build.rs`), and test binaries that embed `CARGO_MANIFEST_DIR`
differ per checkout. Everything from crates.io is restored.
Build `--release` only when the change is about the release build: it is a
second, separate set of every crate, so it doubles the cold build and the
cache's size for something `cargo test` does not run.
### While iterating, run the tests that could have broken
`cargo test --workspace --all-targets` is about 1570 tests, and on a warm build
it takes about 5 seconds of wall time for 6 seconds of CPU (6 cores, already
loaded to about 4 by other lanes, median of seven runs). It used to be a minute
of mostly `thread::sleep`; the sleeps are now waits on the condition itself
(`cctop_core::test_wait`), so what is left is the real ptys and subprocesses,
and the slowest binaries take about a second each. No test asserts a tight
wall-clock margin any more: the few that check `elapsed()` —
`test_wait::tests::a_condition_that_already_holds_costs_no_sleep`,
`yolo::tests::the_hooks_allow_never_waits_long` and
`ssh_master::tests::a_command_that_overruns_is_cut_off`, all in `-p cctop-core`
— bound something meant to be instant by fifty times what it needs. A
full-suite failure on a busy machine is still not evidence until you have
re-run it alone: fork-heavy tests share one process, and a race between them
is not your change.
One such race is worth knowing when you write a test that takes an `flock`:
the lock belongs to the open file description, and a child forked by any
other test thread holds a copy of every open descriptor until it execs. A
lock file this test (or code it called) opened a moment ago can therefore
still be held when the test tries to take it. Take it on a file nothing has
opened yet, as `yolo::tests::switched_on_unlocked` does, or wait for it with
`test_wait`.
The first run after a build can also be several times slower than the next
(#141): 40 s rather than 10, with a handful of tests taking seconds that take
a fraction of one on a rerun. What is known of the cause:
- `recall::tests::recall_finds_the_passage_and_skips_the_caller` used to load
the fetched 30 MB embedding model from `~/.cache/cctop` — cold off the disk on
a first run, and only on a machine that had fetched one. Under test,
`config::CACHE_DIR` is now a temporary directory of the process's own, so no
test reads or writes the real cache.
- `advise::tests::the_ledger_stays_small` takes an `flock` per write and polls
for it every millisecond. A child forked by another test in the same binary
holds an inherited flock until it execs, so under a parallel run with many
forks that wait can add up.
- The `chat::tests::an_opencode_*` tests build sqlite fixtures; the first one
pays for sqlite's first touch.
So a slow first run on its own is not a regression: compare it against a second
run of the same command before blaming any one test.
`tools/targeted-test.sh` maps what you changed to the tests worth running:
```bash
./tools/targeted-test.sh # diff against main, run what it names
./tools/targeted-test.sh crates/ui/src/filter.rs # or name the files yourself
./tools/targeted-test.sh --all # force the full suite
```
A test's module path is its file's module path inside its own crate, so
`crates/ui/src/filter.rs` runs `filter::` in `-p cctop-ui`, and `src/cli.rs`
runs `cli::` in the binary, `-p cctop`. A crate root (`lib.rs`, `main.rs`) runs
that crate's whole suite; `crates/core/build.rs` or anything non-Rust runs
everything. Only the changed file's own crate is tested, not the crates built
on it — that is what the full run at the end is for. Use it while you work and
the full suite once, at the end, on its own.
## Layout
cctop is one binary built from five crates, so that an edit recompiles only
what sits above it:
| `cctop` | `src/` | `main`, the command line, and the commands nothing else calls (`doctor`, `why`, `wait`, `mcp`, `recall`) |
| `cctop-ui` | `crates/ui/` | the terminal dashboard |
| `cctop-serve` | `crates/serve/` | the web server |
| `cctop-core` | `crates/core/` | sessions and their parsers, the cache, pricing, config, processes, hooks, rmux, the shim, and what both faces read and do to a session (the conversation, report, export, handoff, actions) |
| `cctop-tunnel` | `crates/tunnel/` | local ports on public URLs, behind a provider-agnostic `Provider` trait; Cloudflare's quick and named tunnels are the two implementations, speaking the edge's protocol natively |
The dashboard and the server each depend on core and not on each other, and
the binary depends on all three; core depends on the tunnel crate, which
depends on nothing of cctop's and is the one crate whose licence is not plain
MIT (it began as `cloudflare-quick-tunnel`, MIT OR Apache-2.0); the root `Cargo.toml` says why each boundary
is where it is. Nothing in core reaches up: something both faces need belongs
in core. The dashboard starts a server to share its table through a function
the binary hands it (`serve_for_dashboard` in `src/main.rs`).
Core's guards that keep a test off the real machine — no bell on stdout, no
copy to your clipboard, no write over your saved preferences, a runtime
directory of the test's own — ask `cctop_core::under_test()`, and the fixtures
other crates' tests use are `cfg(any(test, feature = "test-support"))`.
`cfg(test)` is only true for core's own tests, so the other crates turn the
feature on from their dev-dependencies. A release build never has it; a binary
built by `cargo test` does, and its `main` switches the guards off before
anything else runs, so it behaves as cctop.
## The `debug` feature
`crates/serve/src/debug.rs` is behind `#[cfg(feature = "debug")]`, which is off by
default and never enabled for a release — so an ordinary build contains neither
the routes nor the strings that name them. That is the condition for having them:
a debug surface reachable in a shipped binary is a debug surface somebody else
can reach, and the serve token is one link away from anyone you shared a page
with.
Three things live behind it, all reachable only from a build that asked:
- `/api/debug/state` and `/api/debug/why` — what the server is holding, and how
it decided which sessions are running. Both are answerable from outside
(`cctop -j`, `cctop why`), but not from the serving process itself, which is
where a disagreement between the page and the terminal would show.
- `/api/debug/fault` — makes subsequent `/api/` responses fail in a chosen way
(`502`, `slow`, `html`, `empty`), or holds the event stream open and silent
(`stall`, what a quick tunnel that does not carry SSE looks like). The pages
have to survive a tunnel whose far end has gone and a proxy answering HTML
where JSON was asked for, and neither can be produced on demand by a correct
server.
- `/api/debug/log?level=io` — turns `CCTOP_LOG` on for a server that was not
started with it.
```bash
cargo run --features debug -- serve --no-token
```
Because the feature is off by default, `cargo clippy --all-targets` and
`cargo test --all-targets` never compile that module — a change to
`crates/serve/src/lib.rs` that breaks the debug routes is green, and nothing finds out
until someone runs it by hand. So `verify` runs both commands a second time
with `--features debug`, and a change that touches those routes should pass both
locally:
```bash
# -D warnings is set in .cargo/config.toml
cargo clippy --all-targets --features debug
cargo test --all-targets --features debug
```
The tests do not exercise the fault routes — arming `slow` sleeps for 30
seconds by design — so the extra run is a compile check, not a timing one. If you
add tests here, keep them off `slow`, or the suite grows half a minute per case.
## cctop is Linux-only
There is one platform, and it is Linux (including WSL). macOS and Windows were
supported once and are not any more: `verify` builds and tests on Linux alone,
and a release ships two statically linked musl archives, x86_64 and aarch64.
Write for Linux directly. A `#[cfg(unix)]` or `#[cfg(target_os = "linux")]`
gate is noise around code that has no other target to be conditional against,
and a stub standing in for a platform that is no longer built is dead code,
which `-D warnings` rejects.
## `cctop hook` must never break the session it watches
`cctop hook` runs inside someone's coding session, many times a minute. Claude
Code reads its exit code as a *decision*: non-zero blocks the tool call and
feeds stderr back to the model. So it exits 0 always, writes nothing to stdout,
and returns inside a deadline — by construction, not by care. See the module
docs in `crates/core/src/hook/mod.rs`.
A hook that fell through to clap would exit non-zero on every fire, so the
`hook` dispatch in `main.rs` is never gated behind anything.
## Conventions
- **`ponytail:` comments** mark a deliberate, documented limit — a thing this
code knowingly does not do. They are not TODOs and do not want fixing without
a reason.
- **Comments say why, not what.** The prose in this codebase explains the
decision behind a line; match that rather than narrating the syntax.
- **Doc comments carry the reasoning** for anything a reader would otherwise
have to reconstruct — especially where two plausible designs existed.
## Design notes
A few things that are less obvious from the code:
- **Token dedup.** Streaming writes the same `requestId` repeatedly with growing
counts. Only the last entry per request is counted; summing them all inflates
totals several-fold.
- **Cache keys carry a pricing generation.** Cached entries hold *computed*
costs, so a refreshed rate table must invalidate them just as an appended
transcript does. Without this, sessions priced before the table loaded report
`$0.00` forever — their transcripts never change again.
- **The cache version is derived, not written.** `build.rs` hashes the shape of
the serialised types, so adding a field to `SessionData` invalidates stale
entries without anyone remembering to bump a number.
- **Threads are excluded from process matching.** Threads share their process's
command line, so every one of them matches the same session and competes to be
picked as the root — nondeterministically. The winner reports its own CPU and
no children.
- **Tail reads.** Context usage and last-tool come from seeking backwards from
EOF, so a live 50 MB transcript costs one 64 KB read per refresh, not a
reparse.
- **Ghost subagents.** Claude Code purges old subagent transcripts but keeps the
`tool_use`/`tool_result` pair in the parent. Those rows are reconstructed and
marked `◌`, with `—` rather than `0` for figures that can no longer be
measured.
- **Collisions compare repository roots, not directories.** A linked worktree
carries its own `.git`, so two agents in two worktrees do not collide while
two in one checkout do. Comparing directories gets both backwards.
- **Remote rows are inert.** A row from `--host` carries `Session::remote`, and
every action that signals a process, deletes a file, opens a pty or reads a
git directory guards on it — all of those are about *this* filesystem.
## Releasing
A release is a merged pull request, and it is always the same one. On every
push to `main`, `.github/workflows/release-plz.yml` runs
[release-plz](https://release-plz.dev), which keeps one pull request open —
labelled `release`, titled `chore: release`, on a `release-plz-…` branch —
that bumps every crate main would release, with `Cargo.lock` to match. It is
rebuilt from scratch whenever main moves, so it is always current and never
needs rebasing.
**Merging it is the release.** That changes the root version, and on a change
of the root version on `main` `release.yml` derives the matching `v<version>`
tag, creates the GitHub release, builds the Linux archives and publishes to
crates.io. There is no separate confirmation step, and `cargo publish` to
crates.io cannot be undone. Do not create a release tag by hand, and do not
let release-plz create one: tagging, the GitHub release and publishing are
release.yml's alone, and `release-plz.toml` switches them off in release-plz.
Before merging:
1. **Write the release's prose at the top of the description**, above the
first line (an invisible marker). One paragraph saying what the release is
for, in the user's terms — the theme, and why the digit that moved moved.
`release.yml` puts it above the generated list of merged pull requests, and
`cctop --update` shows it to everyone who updates. release-plz rewrites the
description whenever main moves, so write it last; left empty, the release
is the generated list alone.
2. **Check CI is green on it.** It runs like on any pull request, because
release-plz opens it with a real account's token (below).
3. **Make it a minor if it should be one.** release-plz bumps the root by a
patch. When behaviour changed in existing installs, set the root version
(`version` under `[workspace.package]` in the root `Cargo.toml`) to the next
minor on the release branch, run `cargo update --workspace` for the lock,
and push both. Do it last too: a commit by anyone but release-plz makes the
next run close that pull request and open a fresh one, without it.
### What gets bumped
The four internal crates, `cctop-tunnel`, `cctop-core`, `cctop-serve` and
`cctop-ui`, each have their own `version` in `crates/*/Cargo.toml`. The root
requires each with a caret on the compatible part of its version under
`[workspace.dependencies]` — `"0.28"`, meaning at least 0.28.0 and below 0.29
— so a published `cctop-ui` keeps building beside a newer `cctop-core` of the
same minor. release-plz bumps one only if it differs from its copy on
crates.io, which is any of:
1. **its files changed**;
2. **its packaged manifest changed** without that — a `[workspace.dependencies]`
entry it uses was bumped, its requirement on an internal crate moved, or a
`[workspace.package]` field it inherits (`edition`, `rust-version`,
`license`…);
3. **an internal crate it depends on takes a breaking bump**, because that
moves its requirement. Whether a crate's public API broke is
[`cargo-semver-checks`](https://github.com/obi1kenobi/cargo-semver-checks)'
answer, against the same crate as published; a crate that broke takes
0.28.x → 0.29.0, and its requirement moves to `"0.29"`. The release pull
request says which crates broke, and what the tool found.
The root `cctop` is bumped whenever anything is: `release.yml` releases on a
change of its version and nothing else, and an internal crate is only reachable
through a `cctop` that requires it.
So a change to `crates/ui` alone bumps `cctop-ui` and `cctop`, one to
`crates/core` that keeps its API bumps `cctop-core` and `cctop`, one that
breaks it bumps core to the next minor and `cctop-serve` and `cctop-ui` by a
patch for the moved requirement, and one to the binary's own `src/` bumps
`cctop` alone. `pub` in these crates exists for use between them rather than as
a designed API, so expect a breaking bump more often than a library would take
one.
The carets let `cargo install cctop` *without* `--locked` pick a newer
compatible core than the one released with it. The published crate carries its
`Cargo.lock`, `cctop --update` and the README both pass `--locked`, and
`cargo-semver-checks` covers the API; what is left is a behaviour change that
kept the API, reaching someone who typed a bare `cargo install cctop`.
- **`cargo-semver-checks` moves with the toolchain.** It reads the rustdoc JSON
the pinned Rust writes, and each release of it understands a range of Rust
versions, so its version sits at the end of `rust-toolchain.toml`, beside
`channel`, and `release-plz.yml` installs that one. A pull request that moves
`channel` checks its release notes and moves that line too when it has to.
- **`publish-crate`** asks the crates.io index which crates are missing at
their current version (`tools/unpublished-crates.sh`) and publishes only
those, dependency order first; the rest are skipped with a notice. A run that
failed part-way can be re-run as it is.
- **To see what release-plz would do** without opening anything, run
`release-plz update` in a scratch clone (it edits the manifests in place) and
`git diff` there. It needs `cargo-semver-checks` at the pinned version on
`PATH`.
### The token release-plz opens the pull request with
A pull request opened with a workflow's own `GITHUB_TOKEN` starts no workflow,
so CI would never run on the release pull request. `release-plz.yml` therefore
uses the repository secret **`RELEASE_PLZ_TOKEN`**, and fails, saying so, when
it is missing. Either of:
- a **fine-grained personal access token** of a maintainer, for this
repository only, with *Contents: read and write* and *Pull requests: read and
write* (and *Metadata: read*, which GitHub adds itself); or
- a **GitHub App** installation token with the same two permissions, minted in
the workflow by `actions/create-github-app-token` — it does not expire with a
person's token, at the cost of an app to keep.
`gh secret set RELEASE_PLZ_TOKEN` stores it. A fine-grained token expires; when
release-plz.yml starts failing on a 401, that is the first thing to renew.
### Name every other pull request after what it changes
The notes GitHub generates are one line per merged PR, and `cctop --update`
prints those lines to everyone who updates — so a PR title is a release note.
`CLAUDE.md` has the full rule and the shapes to avoid; the short version is to
write the sentence you would want someone three versions behind to read. The
release pull request is the one exception, left out of the list by its
`release` label (`.github/release.yml`): its prose goes in its description.
Notes are fetched when someone updates rather than when the release is cut, so a
note that landed badly is still worth fixing: edit the release body on GitHub and
everyone who has not updated yet sees the better one.
### The mirror and the signature
`cctop --update` asks GitHub first and falls back on a Cloudflare Worker,
`worker/`, for both the release JSON and the archives: GitHub rate-limits
anonymous API calls and is sometimes simply down. The release workflow keeps
the Worker in step (`tools/push-release-mirror.sh`), and a mirror failure
never fails a release. The Worker is deployed by Cloudflare Workers Builds
when a change to `worker/` reaches `main` — not by hand — so anything a new
binding in `worker/wrangler.jsonc` names (a bucket, a namespace) has to exist
in the Cloudflare account *before* that change merges.
Each archive is signed with ed25519 before the release is made public
(`tools/sign-release.sh`, with the `RELEASE_SIGNING_KEY` secret), and the
updater checks it against `RELEASE_PUBLIC_KEY` in `crates/core/src/update.rs`
for every download, GitHub's or the mirror's. That is what keeps the mirror's
push token from being a way to ship a binary to everyone. `tools/release-key.sh`
makes the pair once: it stores the private half in the secret without printing
it and prints the public half to paste. Do not run it again for an existing
key — a binary refuses releases signed by any key but the one it carries.
## Refreshing the screenshots
`docs/assets/` holds real captures, not mock-ups. Regenerate them after any
change to the table's columns or the panels:
```bash
cargo build --release
R="--redact YourCompany=Example Inc"
python3 docs/assets/shot.py docs/assets/dashboard.png --size 146x30 $R
python3 docs/assets/shot.py docs/assets/context.png --keys 'Tab*7' --size 146x36 $R
python3 docs/assets/shot.py docs/assets/demo.gif --record docs/assets/demo.cast \
--size 128x30 --scale 1 $R
```
The script drives a real cctop through tmux and rasterises the captured screen
itself, so the images carry whatever is on the machine that made them.
**It scrubs email addresses unconditionally**, because cctop reads the signed-in
account out of each harness's config and prints it in the Info panel — an
address the person taking the screenshot never chose to publish and would not
think to look for. `--redact` adds literals (an employer, a client's project
name). Scrubbing happens on the parsed grid, so a replacement of a different
length cannot shift a column: it is padded or truncated to the same width.
Nothing else is scrubbed. Session titles, working directories and real spend
figures all appear as they are — look at what is in frame before committing.
Three traps the script guards, each of which produced a wrong picture first:
- a multiplexer session named `cctop-*` is adopted by cctop as one of its own
tabs, so it attaches to the terminal it is running in. cctop drives rmux, and
the script drives tmux, so the two no longer collide — the guard stays because
the naming rule is what made it a trap, not which daemon held the session;
- preferring `target/release` over `target/debug` captures whichever is *older*,
which once shipped a screenshot missing two columns added that afternoon;
- an SVG would be smaller and sharper, but cctop draws sparklines with eight-dot
braille (U+2840+) and DejaVu Sans Mono covers only the six-dot block, so those
cells become tofu on any reader whose font agrees. Rasterising pins them;
- DejaVu Sans Mono is a wide face, and at its natural line height the cell is
1.93:1 against the ~2.2 terminals use — every row looks vertically squashed.
The cell is therefore 1.35× the font size, and the ten box and block glyphs
(`─━│┊╭╮╯╰█░`) are drawn as geometry rather than text, because a font's box
characters only span its *own* natural line height and would otherwise leave
the panel borders visibly gapped.
## Agents' git hooks
`tools/git-hooks` holds three hooks that act only inside a Claude Code session
(`CLAUDECODE=1`) and leave a person's commits alone: one adds the co-author
line to an agent's commit, the other two push each commit (and each merge) in the background on a
branch that already tracks the remote (never `main`, never mid-rebase), so an
agent's draft PR is always current. Enable them once per clone:
```bash
git config core.hooksPath tools/git-hooks
```
A fourth, `reference-transaction`, is for a main clone kept bare so that only
worktrees are edited. The files beside such a clone are what a session started
there reads (CLAUDE.md, agents, skills), and git never updates them. The hook
runs `tools/refresh-checkout.sh` whenever a fetch moves `origin/main`, which
brings them up to date unless someone has edited them by hand. The first time,
name the commit they are at:
```bash
tools/refresh-checkout.sh --from <commit> # later runs remember it
```
## The issue loop
GitHub issues are a work queue: an issue filed from anywhere, a phone
included, is picked up by agents — but only while a Claude Code session is
running the loop on a machine with a checkout. Nothing on GitHub's side starts
one. To start it, open Claude Code in the checkout and run:
```text
/loop /issue-loop:issues
```
With no interval the loop paces itself (see the `issue-loop` plugin's `issues` skill,
"Under /loop"): each pass spawns solvers in the background, and their finishing
wakes the loop again. When nothing is running and nothing is queued it looks
again in about 20 minutes — soon enough that an issue filed from a phone is
started within the half hour, without polling GitHub every minute for a queue
that is usually empty. Press `Esc` to stop it. A self-paced loop is not
restored by `claude --resume`, and like any recurring task it expires after
seven days, so run `/loop /issue-loop:issues` again after either.
What it picks up is decided by labels, the table in the skill:
| `agent-ready` | written and waiting for a solver — the only label that starts new work |
| `agent-working` | a solver has it, with a draft PR from `issue-<N>` |
| `agent-question` | the solver asked on the issue and stopped; your reply resumes it |
| `agent-pr` | the PR is ready for review; review comments send a solver back |
So an issue filed by hand needs the `agent-ready` label to be worked on, and an
unlabelled one is left alone. `/issue-loop:issues <one-line request>` files one with the
issue-writer agent, which writes it up and adds the label. Merging and
releasing stay with you: the loop never merges a PR or bumps a version.