Triage bot and PR-based claims (#2397)

* Claim bot: a PR referencing an issue claims it

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01TPWBBSRPfPYWgrrhbznewR

* Triage bot: label new issues and PRs, /triage, backfill

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01TPWBBSRPfPYWgrrhbznewR

* Docs: a draft PR is the claim; labels and triage

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01TPWBBSRPfPYWgrrhbznewR

* Triage bot: start a runner only for events it acts on

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01TPWBBSRPfPYWgrrhbznewR

---------

Co-authored-by: jyviko <[email protected]>
Co-authored-by: Claude Opus 5.5 <[email protected]>

CONTRIBUTING.md

@@ -258,9 +258,10 @@ and a fresh CI run:
      open a **draft** PR titled `<summary> (#N)`, e.g. `Fillet: variable radius along a chain (#123)`.
    - **The lowest-numbered open PR for an issue wins.** If yours lost, close it (or offer to help
      on the other one).
-   - Then comment `/claim` on the issue so the bot records the claimant and adds the `in progress`
-     label. **Do both:** the draft PR establishes ownership and `/claim` marks the issue as taken.
-     Reference `#N` in the PR so the bot can find it; a comment alone does not replace the draft PR.
+   - The bot records the claim when the PR is opened: it assigns you, adds `in progress` and
+     says so on the issue. It reads `#N` in the PR title and `Fixes #N` in the body. If someone
+     already holds the issue, or an older open PR references it, it says so on your PR instead.
+   - Want to stake a claim before you have a branch? Comment `/claim` on the issue (below).
    - Push work in progress at least daily. A draft with no pushes for 72 hours may be taken over:
      comment on it first, then open your own claim.
    - Mark the PR ready for review when it is done.
@@ -270,10 +271,10 @@ and a fresh CI run:
 4. Reference the issue (`Fixes #12`). In the PR, say what you tested and how. For geometry work, include the measured numbers (and
    the expected ones).
 
-The `/claim` bot assigns you, adds the `in progress` label, and replies with its automatic cleanup
+Commenting `/claim` assigns you, adds the `in progress` label, and replies with its automatic cleanup
 deadline. It frees a claim with no linked PR after 72 hours, or a claim with a PR after 14 days
 without pushes. These automatic cleanup deadlines are separate from the daily progress and
-72-hour takeover policy above; follow the draft PR then `/claim` sequence before starting work.
+72-hour takeover policy above. A draft PR that references the issue claims it the same way.
 `/unclaim` releases the bot claim early (only you or a maintainer can). Issues a maintainer has
 taken are never freed automatically.
 
@@ -303,6 +304,21 @@ owning one area, with a human setting direction and reporting bugs. Their workin
 [AGENTS.md](AGENTS.md). Human contributors are just as welcome. Use whatever tools you like, as
 long as the change meets the rules above.
 
+## Labels and triage
+
+The triage bot labels every new issue and PR (`.github/workflows/triage.yml`). It only adds labels;
+correct them freely and it won't put them back.
+
+- **PRs** get `area:*` from the paths they change (`crates/kernel` and `crates/geom` →
+  `area:kernel`, `crates/ui-egui` and the apps → `area:ui`, `.github/`, `scripts/`, `docs/` →
+  `area:infra`, and so on).
+- **Issues** get `bug` (in-app reports and the bug template), `enhancement` (feature requests),
+  `priority:P1` for crashes, and an `area:*` from the title or the reported command. Until it has
+  a priority, an issue carries `needs-triage`; setting a priority removes it.
+- **Maintainers** comment `/triage area:kernel P1` (any existing label; `P0`–`P3` for a
+  priority, which replaces the old one; `-label` removes one) to sort an issue or PR.
+- `needs-triage` is the queue: [open issues with it](https://github.com/tangency-labs/solidcraft/issues?q=is%3Aopen+label%3Aneeds-triage).
+
 ## Where help is wanted most
 
 **Kernel speed (slow fillets, booleans, STEP):** please don't rewrite the current kernel code for speed; it is being replaced by [solidcore](https://github.com/bherbruck/solidcore) ([progress](https://tangency-labs.github.io/solidcore/)). Report slow cases with a file under the `kernel-perf` label, and put kernel effort into solidcore instead. See [#1597](https://github.com/tangency-labs/solidcraft/issues/1597).