docs: align Copilot instructions with CLAUDE.md

.github/copilot-instructions.md

@@ -10,6 +10,7 @@ A companion guide `CLAUDE.md` at the repo root carries the shared rules for Clau
 - **Repository prose follows the Google developer documentation style guide** - `docs/`, `README.md`, `agentic/docs/`, changelog entries, and PR/issue text use [Google style](https://developers.google.com/style) (sentence-case headings, second person, numbered procedures); the concrete rules and the house-style exception (`docs/reference/style-guide.md` governs website/brand surfaces) live in the `write-docs` skill (`.claude/skills/write-docs/SKILL.md`). Existing docs migrate on touch, not via bulk rewrites.
 - **Changelog and releases** - see [Changelog + releases](#changelog--releases) below: every PR adds a fragment under `changelog.d/` and adds nothing to `CHANGELOG.md`, a release folds the fragments and bumps the version files via a PR, and the GitHub release is that section condensed, never copied. When reviewing a non-exempt PR that lacks a fragment — or that ADDS a bullet to `[Unreleased]` — flag it; correcting the wording of a bullet already there is allowed and must not be flagged.
 - **Never echo secret values into transcripts or logs** - Verify secrets by exit code or metadata, never by printing them.
+- **Fix small build/test blockers directly, even when out of scope** - If a typecheck error, failing test, lint failure, or other small pipeline blocker shows up while you work on something unrelated, fix it in the same PR or a tiny follow-up — never leave it parked as "pre-existing" or "out of scope". A latent error that doesn't surface locally silently breaks the next Cloud Build, which deploys nothing while every PR check looks green. The bar: if the fix is under ~20 lines and obviously correct, make it; if it would expand scope meaningfully, ask first rather than deferring silently.
 - **Structural fix over symptomatic fix** - When a cheap symptomatic fix and a correct structural fix compete, take the structural one: fix the cause, never mute the alarm. Never modify working code to make a broken test pass — fix the test or flag it.
 - **Never manually merge a pipeline PR, and never bypass the pipeline** - Specifications and implementations go through the GitHub Actions workflows: `spec-create.yml` writes `plots/{spec-id}/specification.md` and `.yaml`, `impl-merge.yml` merges implementation PRs and creates their `metadata/*.yaml`, promotes the preview images to GCS and sets the `impl:{library}:done` label. Merging one by hand skips all of that and leaves `quality_score: null`, no review data, missing GCS images and the issue open. So: never write those files by hand, never run `gh pr merge` on a spec or implementation PR, and add the `approved` label to the **issue**, never to the PR. The full DON'T/DO table is in `CLAUDE.md`. Ordinary (non-pipeline) PRs are merged by the repository owner, not by an agent.
 
@@ -23,7 +24,7 @@ A companion guide `CLAUDE.md` at the repo root carries the shared rules for Clau
 
 **Good tasks for Copilot:**
 - Bug fixes in existing plot implementations
-- Adding new plot types following existing patterns
+- Proposing new plot types as a `spec-request` issue (the pipeline writes the spec and implementations; see Important Rules)
 - Updating documentation
 - Writing or improving unit tests
 - Code refactoring within established patterns
@@ -314,7 +315,7 @@ uv run alembic upgrade head
 
 ### Known Limitations
 
-- **Package Manager**: `uv` may not be available in all environments. Fallback to `pip` if needed.
+- **Package Manager**: Python dependencies are managed with `uv` only — run everything through `uv sync` and `uv run`, never `pip`. If `uv` is missing, install `uv` itself ([installation guide](https://docs.astral.sh/uv/getting-started/installation/)) instead of falling back to `pip`.
 - **External Dependencies**: Some domains may be blocked. If encountering network issues, document them in the PR.
 - **Database**: Cloud SQL requires proper credentials. Use `.env.example` as template for local development.
 
@@ -327,7 +328,7 @@ uv run alembic upgrade head
 
 ### Common Issues
 
-- **Import errors**: Run `uv sync --all-extras` or `pip install -e ".[dev]"` to install dependencies
-- **Test failures**: Ensure you're testing only changes related to your task, not pre-existing issues
+- **Import errors**: Run `uv sync --all-extras` to install dependencies
+- **Test failures**: Fix a small failure you run into even when your task did not cause it (see "Fix small build/test blockers directly" under Important Rules); ask before a fix that would expand the PR's scope meaningfully
 - **Linting failures**: Run `uv run ruff check . --fix` to auto-fix common issues
 - **Type checking**: Add type hints using standard Python typing (e.g., `list[str]`, `dict[str, int]`)

CLAUDE.md

@@ -88,7 +88,7 @@ Known gaps with NO verification loop yet (reason through carefully and say so in
 
 - **Frontend**: Use `yarn` (not npm). Run `cd app && yarn` for installs, `cd app && yarn dev` for dev server.
 - **Backend**: Python dependencies managed via `pyproject.toml`. For transitive dependencies, update the lock file directly — do not add constraints to `pyproject.toml`.
-- **Scripts**: Use `uv run` for running Python scripts.
+- **Scripts**: Use `uv run` for running Python scripts. Python tooling is `uv` only — `uv sync` and `uv run`, never `pip`; if `uv` is missing, install `uv` itself instead of falling back to `pip`.
 
 ## Claude Code Configuration
 

changelog.d/align-copilot-instructions.md

@@ -0,0 +1,9 @@
+### Changed
+
+- **Copilot instructions agree with CLAUDE.md.** `.github/copilot-instructions.md`
+  now carries the "fix small build/test blockers directly, even when out of
+  scope" rule (under ~20 lines, ask first above that) instead of telling Copilot
+  to leave pre-existing failures alone, drops the `pip` fallback in favour of
+  `uv` only (now stated in both guides), and lists new plot types as a
+  `spec-request` issue rather than a hand-written implementation. The
+  instruction tests pin both rules on both sides. (#12188)

tests/unit/test_agent_instructions.py

@@ -307,6 +307,16 @@ def test_every_named_skill_exists() -> None:
     "a release is condensed, never copied": ["condensed, never copied", "agentic/commands/release.md"],
     "never echo secret values": ["never echo secret"],
     "structural fix over symptomatic fix": ["structural fix over symptomatic fix"],
+    # The obligation (fix it, even out of scope) AND its limit (the ~20-line bar,
+    # ask first above it). Copilot's guide used to say the opposite — test only
+    # your own changes, leave pre-existing failures alone — until 2026-10-15.
+    "fix small build/test blockers, ask first if larger": [
+        "fix small build/test blockers directly, even when out of scope",
+        "~20 lines",
+        "ask first rather than deferring silently",
+    ],
+    # Owner decision 2026-10-15: no `pip` fallback for either audience.
+    "python tooling is uv only": ["`uv` only", "never `pip`", "instead of falling back to `pip`"],
     # The repository's most consequential rule, and the one an agent that opens
     # and edits PRs is most able to break: specs and implementations go through
     # the workflows, and their PRs are merged by `impl-merge`, never by hand.