evals: parent-side shard skipping — a one-test diff runs 3 of 44 shards

The sharded runner spawned every shard regardless of diff; only the
child self-skipped, so a typical single-skill change still paid 44 Bun
boots + container-equivalent setup for shards with zero selected tests.
The parent now computes selection once (mirroring e2e-helpers exactly:
EVALS_ALL -> run-all, empty union -> run-all, git errors propagate the
fail-closed throw) and drops shards where no selected test name maps in.

Mapping = quoted E2E map keys in the file's source UNION keys whose dep
list registers the file (constructed-name families need the second
direction). FAIL-OPEN everywhere it matters: run-all, non-skill-e2e
files, unreadable source, zero mapped names all keep the shard — the
child filter stays authoritative, so a parent bug can only run extra.

New taxonomy status skipped-by-diff (never conflated with
never-started); selection banner prints once; --list is selection-aware.
C6 lands in the same commit: a HARD tier-alignment test — every paid
skill-e2e file must be parent-mappable or provably fail-open-safe.
Note: this change-set's 14 dep-list registrations in touchfiles-data.ts
rode along in f945c841 (concurrent-agent staging); they belong to this
change logically.

Demo: selection of one test -> 'running 3 of 44 shards, 41
skipped-by-diff'. 13 new $0 tests via injected seams.

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

test/e2e-tier-alignment.test.ts

@@ -20,6 +20,8 @@ import { describe, test, expect } from 'bun:test';
 import { readdirSync, readFileSync } from 'fs';
 import * as path from 'path';
 import { E2E_TOUCHFILES, E2E_TIERS, LLM_JUDGE_TOUCHFILES } from './helpers/touchfiles';
+import { isPaidTestFile } from './helpers/paid-test-set';
+import { knownTestNamesInSource, PARENT_MAPPER_TEST_NAMES } from '../scripts/test-paid-shards';
 
 const TEST_DIR = import.meta.dir;
 // Both quote styles — a mechanical refactor to double quotes must not
@@ -88,4 +90,47 @@ describe('E2E tier alignment (touchfiles declaration vs test self-gate)', () =>
 
     expect(misaligned).toEqual([]);
   });
+
+  // HARD invariant (C6): the paid sharded runner skips a skill-e2e shard when
+  // none of the file's MAPPED test names (E2E map keys quoted in its source,
+  // union E2E map keys whose dep list registers the file) are diff-selected.
+  // A skill-e2e file the mapper cannot see at all is only safe if it provably
+  // opts out of name-based selection: it must not touch the e2e-helpers
+  // selection surface (describeIfSelected / runSkillTest / selectedTests) AND
+  // it must carry an explicit whole-file EVALS_TIER self-gate (the child-side
+  // gate that makes the parent's fail-open keep semantically correct).
+  //
+  // Anything else is an invisible-test-names hole: the parent could drop a
+  // shard whose child would have run real work. Fix by either quoting the
+  // test's E2E map key as a string literal in the file, or adding the file's
+  // path to its key's dep list in test/helpers/touchfiles-data.ts.
+  test('every paid skill-e2e file is visible to the parent diff mapper (or provably fail-open-safe)', () => {
+    const invisible: string[] = [];
+
+    for (const file of testFiles) {
+      const repoPath = `test/${file}`;
+      if (!isPaidTestFile(repoPath)) continue;
+      const content = readFileSync(path.join(TEST_DIR, file), 'utf-8');
+
+      const quoted = knownTestNamesInSource(content, PARENT_MAPPER_TEST_NAMES);
+      const registered = Object.keys(E2E_TOUCHFILES).filter((k) => E2E_TOUCHFILES[k].includes(repoPath));
+      if (quoted.length + registered.length > 0) continue; // parent-mappable
+
+      const usesNameSelection = /\b(describeIfSelected|runSkillTest|selectedTests)\b/.test(content);
+      const selfGated = /EVALS_TIER\s*===\s*['"](gate|periodic)['"]/.test(content);
+      if (!usesNameSelection && selfGated) continue; // fail-open-safe standalone
+
+      invisible.push(
+        `${repoPath}: invisible to the parent diff mapper — no E2E map key quoted in the file, `
+        + 'not registered in any E2E_TOUCHFILES dep list, and it '
+        + (usesNameSelection
+          ? 'uses name-based selection (describeIfSelected/runSkillTest/selectedTests)'
+          : 'has no whole-file EVALS_TIER self-gate')
+        + '. Quote the test\'s E2E map key as a string literal, or add this file path to its '
+        + 'key\'s dep list in test/helpers/touchfiles-data.ts.',
+      );
+    }
+
+    expect(invisible).toEqual([]);
+  });
 });