fix: let a removal fixture actually build the thing it claims still builds

FE-GATE-020 proves a capability can be removed by rebuilding the whole project
without it. The fixture it built could not get that far, and the failures all
came from the fixture rather than from anything about removability.

It was not a repository. The supply-chain inventory is defined as the tracked
file set, so it asks `git ls-files` what the project contains; with no
repository to ask, generation failed and took every provider suite down with
it. It is now initialised on preparation and committed after the removal — not
before, or the index would still list the files the removal deleted.

It had no `.gitignore`, so once it did have a repository, every generated
artifact and every linked module landed in the index and the inventory refused
the fixture for tracked and generated paths colliding. It carries the ignore
rules now, and therefore records the same tracked set as the repository it was
copied from.

Each removal script kept its own copy-target list and they had drifted: the
reference-feature fixture omitted `playwright.capabilities.config.ts`, which the
inventory requires. There is one list now. It also gained the install and
workspace identity — `.npmrc`, the lockfile, the workspace file — without which
the fixture is a different project, and the release evidence a candidate is
assembled from, without which no candidate can be built at all.

A tracked root the removal deletes is no longer required of the result: the
optional-recipe fixture deletes `recipes/`, and the inventory policy demanded
it back. Roots that are gone are pruned from the fixture's policy.

Two smaller causes. A platform integration file asserted the reference feature's
own route ids, so removing the feature left it importing a deleted module —
typecheck, the test run, coverage and the residue scan all failed on that one
misplaced assertion, which now lives in the feature's test tree. And the
canonical exact-count authority was re-imposed on a contract the fixture
deliberately reduces, failing the fixture for the reduction it exists to prove;
`CI_CONTRACT_MODE` already marked those runs and is now honoured by default.

The reference-feature fixture goes from failing before its first assertion to
1,612 passing with one failure, and that one is the live process-tree
observation test already red on the main tree.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/unit/ci-artifact-contract.test.ts

@@ -20,6 +20,7 @@ import {
 } from "../../scripts/lib/ci-artifact-validator.ts";
 import { writeCiGateLogAtomic } from "../../scripts/lib/ci-gate-log.ts";
 import { linkFixtureNodeModules } from "../../scripts/lib/fixture-node-modules.ts";
+import { copyReleaseEvidenceTree } from "../../scripts/lib/removal-fixture.ts";
 import { captureCiCandidateArchive, verifyCiCandidateArchive } from "../../scripts/lib/ci-candidate-archive.ts";
 import {
   CANDIDATE_ARCHIVE_USAGE,
@@ -2153,10 +2154,17 @@ async function ensureProviderBaseFixture(): Promise<string> {
       return ![".release", "artifacts", "dist", "node_modules"].includes(first ?? "");
     },
   });
-  await cp(path.join(sourceRoot, "artifacts"), path.join(root, "artifacts"), {
-    recursive: true,
-  });
-  await rm(path.join(root, "artifacts/release"), { recursive: true, force: true });
+  // The release evidence, minus the trace and Storybook trees. Copying the
+  // whole `artifacts/` directory pulled ~28MB of test output into every
+  // provider fixture; sharing the copier with the removal fixture is also what
+  // makes both fixtures contain the same evidence.
+  // `artifacts/release` travels with the fixture rather than being deleted and
+  // rebuilt. Supply-chain generation runs before the candidate is created and
+  // validates the release evidence paths, so deleting them made that step
+  // depend on a previous local run having left them behind — which is why this
+  // fixture only worked in a workspace that had already built a candidate. The
+  // build chain overwrites them anyway.
+  await copyReleaseEvidenceTree(sourceRoot, root);
   await linkFixtureNodeModules(root, sourceRoot);
   const git = spawnSync("git", ["show", "-s", "--format=%H%n%ct", "HEAD"], {
     cwd: sourceRoot,