---
name: coding-law
description: Use before the first edit of any file under functions/, scripts/, migrations/, workers/, apps-script/, .claude/skills/, .agents/skills/, schema.sql or wrangler.toml — and again immediately before every git commit. Take a hash when work starts, submit a hash when work commits. Prevents two agents from silently overwriting each other with individually valid commits.
---

# Coding Law — a hash to start, a hash to commit

## The failure this exists to stop

Two agents read the same file at the same version. Both edit from that version. The second to commit
erases the first one's work. Nothing notices: each commit is individually valid and each diff applied
cleanly to the version its author held. The loss surfaces days later as "why is that fix gone?".

Claiming a file does not fix this. A claim says *I am working here*. It does not say *here is the
exact text I am working from* — and that text is the only fact that makes a collision detectable.

## The procedure

**1. Read the files you are going to change.** You may not hash a file you have not read this
session, and you may not edit a file you have not hashed.

**2. Hash them.**
```bash
shasum -a 256 functions/a/[slug].js functions/_lib/article_ledger.js
```

**3. Open the lease — before your first edit.**
```bash
curl -s -X POST https://miscsubjects.com/api/coding-law/start \
  -H 'content-type: application/json' \
  -d '{"agent":"<yours>:<session prefix>","intent":"<one line>",
       "files":[{"path":"functions/a/[slug].js","base_sha":"<sha>"}]}'
```
Keep the `lease_id`.

**4. Edit.**

**5. Hash again, and close the lease — immediately before `git commit`.**
```bash
curl -s -X POST https://miscsubjects.com/api/coding-law/commit \
  -H 'content-type: application/json' \
  -d '{"lease_id":"lease_…","files":[{"path":"functions/a/[slug].js","new_sha":"<sha>"}]}'
```

**6. Read the answer.**
- `200 {"state":"committed"}` — commit to git and ship.
- `409 {"error":"overwrite_refused"}` — another agent committed that file after you read it. **Your
  commit was about to erase their work.** Re-read the file as it now stands, redo your edit on the new
  text, open a fresh lease, and repeat. Never force. Never retry the same body.

## Scope

Enforced: `functions/`, `scripts/`, `migrations/`, `workers/`, `apps-script/`, `public/`,
`.claude/skills/`, `.agents/skills/`, `schema.sql`, `wrangler.toml`.

Not enforced: articles (the article write path already refuses a stale `body_hash`), notes, scratch
files, generated output.

## Obligation

`scripts/check-coding-law.mjs` runs in the pre phase of every deploy. A changed code file with no
committed lease matching its current contents fails the ship and prints the two calls above.

**If the gate refuses you, the artifact is wrong — not the gate.** Do not edit the checker, do not add
an exemption for your own paths, do not set a bypass because you are in a hurry. That is how a working
invariant becomes a decorative one.

## Red flags — stop and lease

- "I'll just patch this one line."
- "Nobody else is in this file right now."
- "I'll lease it after I see if the change works."
- Reaching for Edit or Write on a code path with no `lease_id` in your context.
- A 409 you are about to retry unchanged.

## Verify

Before the first edit: read ✓ → hash ✓ → `start` returned a `lease_id` ✓.
Before every commit: hash ✓ → `commit` returned 200 ✓ → `git commit`.

## Related

- [Shared Write Law](../shared-write-law/SKILL.md) — the file claim. Complementary: the claim says who,
  this says from what version. Both, not either.
- Live law: https://miscsubjects.com/a/coding-law
- The chain: https://miscsubjects.com/api/coding-law/leases