Map: area globs for every code file and test, and a CI check that fails on a gap #343

Part of epic #337 (linked as parent). The owner approved the epic and all its batches on 2026-10-10; this child is batch 2 and inherits that approval.

User story

As the owner, I want CI to fail when a code file or an e2e test belongs to no area, so that test selection never skips code silently.

Acceptance criteria

• The map check fails and names each tracked code file that no area glob matches.
• The map check fails and names each row test that resolves to no area.
• The map check fails and names each Test outside the features, contract and coverage packages.
• The map check fails and names each area that selects no feature test, except reserved and journey-only areas.
• The map check fails and names each app build file that maps only to no-test.
• FEATURES.md defines the area grammar, glob grammar, reserved areas and journey-only in plain text.

What I'd notice: nothing day to day. A PR that adds an unmapped file or test fails CI and names it.

Tasks

• AreaMap, ParseAreaMap, GlobMatch, AreasOf, IsTestOnly in e2e/coverage/areas.go.
• Rules M1 to M4 and the syntax checks in e2e/coverage/maprules.go, wired into TestFeatureMapCoverage.
• Reserved areas every-test and no-test, globs for every unmapped tracked file, presence on every gated goal, and the grammar section in docs/FEATURES.md.
• Rules table in docs/testing.md.
• Tests from these criteria: maprules_test.go with a fixture repo.

Contract

The planner's contract is the comment on #337, sections 1 and 3 and child A. Clause 2: no (tightens only).

Ownership:

• dev: docs/FEATURES.md, e2e/coverage/areas.go (new), e2e/coverage/maprules.go (new), e2e/coverage/coverage.go (wiring), docs/testing.md (rules table)
• test-writer: e2e/coverage/maprules_test.go, e2e/coverage/testdata/repo/

Budget: 7 files, about 600 lines.

Waits: none; the map check is a pure function of the checkout and go list.

Decisions made for the owner

• See the contract comment on Epic: PRs run only the e2e tests their change affects, with a full run at epic close #337.
• e2e/coverage/**, cmd/testmcp/** and cmd/testservice/** sit in no-test: the coverage package always runs under selection, and no e2e test builds the probe binaries.
• internal/relayfs/** maps to sessions and audit, the areas of its two importers (review round 1).
• cmd/relay/admin_ops.go and cmd/relay/admin_read_ops.go dispatch admin doors across many goals, so they map to every-test (review round 1).
• M4 lists the union of the relaytest build and the untagged release build, so release-only files are checked too (review round 1).
• With no .git at the root the map rules are skipped with an info finding, never silently.