docs(pr-review): coverage-delta semantics, migrated-area redirects, and the campaign-hotspots channel

[matthewevans]

The 24/7 review loop and contribution handler now know: honest coverage
decreases are acceptable (bucket-based gate, only engine_regress is fatal;
marker-name collision trap); migrated-area conformance is a REDIRECT lens
backed by gates, not an extra rejection layer; generated-file dirt, export
nondeterminism, and maintainer-caused staleness are never contributor burden.
Adds the sweep-start read of .agents/pr-review/campaign-hotspots.toml
(lead-maintained, untracked).

[gemini-code-assist]

Code Review

This pull request updates the PR contribution and review loop skills to document guidelines on migrated-area conformance, coverage-delta semantics, and contributor friction, as well as refining the criteria for 'enhancement' and 'feature' labels. The review feedback suggests replacing non-ASCII characters (such as ellipses and arrows) and curly quotes with standard ASCII equivalents to ensure compatibility across different editors and parsers.

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[gemini-code-assist]

Use standard ASCII ellipsis ... instead of the non-ASCII ellipsis character … to ensure maximum compatibility across different editors, terminals, and parsers.

Suggested change

**An honest coverage decrease is acceptable — never ask a contributor to "restore" it.** A parser change that converts a silently-swallowed clause into an explicit `Effect::Unimplemented` moves cards from lying-green to honest-red; that is an improvement, and the campaign's coverage-honesty policy explicitly permits the count to drop. The CI coverage-regression gate is **bucket-based, not count-based**: the only fatal bucket is `engine_regress` — a card LOSING a handler the baseline marked supported. Any number of honest supported→unsupported flips with new marker names passes. One trap to check when a PR introduces new `Effect::unimplemented(name, …)` markers: the name must not case-insensitively collide with a baseline-supported handler name (the current baseline set is seven generic names, e.g. `Effect:choose`, `Effect:have`) — a collision trips a false-fatal `engine_regress` in the merge queue.

**An honest coverage decrease is acceptable — never ask a contributor to "restore" it.** A parser change that converts a silently-swallowed clause into an explicit `Effect::Unimplemented` moves cards from lying-green to honest-red; that is an improvement, and the campaign's coverage-honesty policy explicitly permits the count to drop. The CI coverage-regression gate is **bucket-based, not count-based**: the only fatal bucket is `engine_regress` — a card LOSING a handler the baseline marked supported. Any number of honest supported→unsupported flips with new marker names passes. One trap to check when a PR introduces new `Effect::unimplemented(name, ...)` markers: the name must not case-insensitively collide with a baseline-supported handler name (the current baseline set is seven generic names, e.g. `Effect:choose`, `Effect:have`) — a collision trips a false-fatal `engine_regress` in the merge queue.

[gemini-code-assist]

Use standard ASCII arrow -> instead of the non-ASCII arrow character → to ensure maximum compatibility across different editors, terminals, and parsers.

Suggested change

At sweep start, read `.agents/pr-review/campaign-hotspots.toml` if present (lead-maintained, untracked, updated at campaign routing/ship events). It lists: migrated areas with the rule now in force and the REDIRECT pointer for authors; coverage-delta semantics (an honest coverage DECREASE — silent swallows converted to explicit `Effect::Unimplemented` — is acceptable and must never be "restored"; in CI only the `engine_regress` bucket, a card LOSING a previously-supported handler, is fatal); diff content outside the contributor's control (generated-file dirt, export nondeterminism, staleness caused by maintainer-side churn — strip/normalize/rebase these yourself, never request changes for them); and files owned by in-flight campaign units (a contributor PR racing those files → hold + surface to the maintainer). Hotspots inform routing and comment content; they are NOT an additional review gate — if a hotspot prohibition reaches review without CI redding it, that is a gate gap: file it, don't make the contributor absorb the miss.

At sweep start, read `.agents/pr-review/campaign-hotspots.toml` if present (lead-maintained, untracked, updated at campaign routing/ship events). It lists: migrated areas with the rule now in force and the REDIRECT pointer for authors; coverage-delta semantics (an honest coverage DECREASE — silent swallows converted to explicit `Effect::Unimplemented` — is acceptable and must never be "restore"; in CI only the `engine_regress` bucket, a card LOSING a previously-supported handler, is fatal); diff content outside the contributor's control (generated-file dirt, export nondeterminism, staleness caused by maintainer-side churn — strip/normalize/rebase these yourself, never request changes for them); and files owned by in-flight campaign units (a contributor PR racing those files -> hold + surface to the maintainer). Hotspots inform routing and comment content; they are NOT an additional review gate — if a hotspot prohibition reaches review without CI redding it, that is a gate gap: file it, don't make the contributor absorb the miss.

[gemini-code-assist]

Use standard straight quotes " instead of curly quotes “ and ” to maintain consistent formatting and avoid potential encoding issues.

Suggested change

	**Evaluate every test-only PR independently.** A series of narrowly scoped test PRs earns no collective presumption of value: each PR must cite the specific existing coverage it does *not* duplicate, name the distinct regression it guards, and demonstrate a failure against the plausible pre-fix or wrong implementation. “This is another test for the same area” is not merge value.
	**Evaluate every test-only PR independently.** A series of narrowly scoped test PRs earns no collective presumption of value: each PR must cite the specific existing coverage it does *not* duplicate, name the distinct regression it guards, and demonstrate a failure against the plausible pre-fix or wrong implementation. "This is another test for the same area" is not merge value.