test: tier-1 live-fire E2E for context-save + context-restore

8 periodic-tier E2E tests that spawn claude -p with the Skill tool
enabled and the skill installed in .claude/skills/. These exercise
the ROUTING path — the actual thing that broke with /checkpoint.
Prior tests hand-fed the Save section as a prompt; these invoke the
slash-command for real and verify the Skill tool was called.

Tests (~$0.20-$0.40 each, ~$2 total per run):

1. context-save-routing
   Prompts "/context-save wintermute progress". Asserts the Skill
   tool was invoked with skill:"context-save" AND a file landed in
   the checkpoints dir. Guards against future upstream collisions
   (if Claude Code ships /context-save as a built-in, this fails).

2. context-save-then-restore-roundtrip
   Two slash commands in one session: /context-save <marker>, then
   /context-restore. Asserts both Skill invocations happened AND
   restore output contains the magic marker from the save.

3. context-restore-fragment-match
   Seeds three saves (alpha, middle-payments, omega). Runs
   /context-restore payments. Asserts the payments file loaded and
   the other two did NOT leak into output. Proves fragment-matching
   works (previously untested — we only tested "newest" default).

4. context-restore-empty-state
   No saves seeded. /context-restore should produce a graceful
   "no saved contexts yet"-style message, not crash or list cwd.

5. context-restore-list-delegates
   /context-restore list should redirect to /context-save list
   (our explicit design: list lives on the save side). Asserts
   the output mentions "context-save list".

6. context-restore-legacy-compat
   Seeds a pre-rename save file (old /checkpoint format) in the
   checkpoints/ dir. Runs /context-restore. Asserts the legacy
   content loads cleanly. Proves the storage-path stability
   promise (users' old saves still work).

7. context-save-list-current-branch
   Seeds saves on 3 branches (main, feat/alpha, feat/beta).
   Current branch is main. Asserts list shows main, hides others.

8. context-save-list-all-branches
   Same seed. /context-save list --all. Asserts all 3 branches
   show up in output.

touchfiles.ts: all 8 registered in both E2E_TOUCHFILES and E2E_TIERS
as 'periodic'. Touchfile deps scoped per-test (save-only tests don't
run when only context-restore changes, etc.).

Coverage jump: smoke-test level (~5/10) → truly E2E (~9.5/10) for the
context-skills surface area. Combined with the 21 Tier-2 hardening
tests (free, 142ms) from the prior commit, every non-trivial code
path has either a live-fire assertion or a bash-level unit test.

test/helpers/touchfiles.ts

@@ -116,6 +116,19 @@ export const E2E_TOUCHFILES: Record<string, string[]> = {
   'context-save-writes-file':       ['context-save/**', 'bin/gstack-slug'],
   'context-restore-loads-latest':   ['context-restore/**', 'bin/gstack-slug'],
 
+  // Context skills E2E (live-fire, Skill-tool routing path) — see
+  // test/skill-e2e-context-skills.test.ts. These are periodic-tier because
+  // each one spawns claude -p and costs ~$0.20-$0.40. Collectively they
+  // verify the thing the /checkpoint → /context-save rename was for.
+  'context-save-routing':                  ['context-save/**', 'scripts/resolvers/preamble.ts'],
+  'context-save-then-restore-roundtrip':   ['context-save/**', 'context-restore/**', 'bin/gstack-slug'],
+  'context-restore-fragment-match':        ['context-restore/**'],
+  'context-restore-empty-state':           ['context-restore/**'],
+  'context-restore-list-delegates':        ['context-restore/**'],
+  'context-restore-legacy-compat':         ['context-restore/**'],
+  'context-save-list-current-branch':      ['context-save/**'],
+  'context-save-list-all-branches':        ['context-save/**'],
+
   // Document-release
   'document-release': ['document-release/**'],
 
@@ -259,6 +272,16 @@ export const E2E_TIERS: Record<string, 'gate' | 'periodic'> = {
   'context-save-writes-file': 'gate',              // /context-save writes a file
   'context-restore-loads-latest': 'gate',          // Cross-branch newest-by-filename restore
 
+  // Context skills live-fire — periodic (each test spawns claude -p, ~$0.20-$0.40)
+  'context-save-routing': 'periodic',              // Proves /context-save routes via Skill tool
+  'context-save-then-restore-roundtrip': 'periodic', // Full cycle in one session
+  'context-restore-fragment-match': 'periodic',    // /context-restore <fragment>
+  'context-restore-empty-state': 'periodic',       // Graceful zero-saves message
+  'context-restore-list-delegates': 'periodic',    // /context-restore list redirect
+  'context-restore-legacy-compat': 'periodic',     // Pre-rename files still load
+  'context-save-list-current-branch': 'periodic',  // Default branch filter
+  'context-save-list-all-branches': 'periodic',    // --all flag
+
   // Ship — gate (end-to-end ship path)
   'ship-base-branch': 'gate',
   'ship-local-workflow': 'gate',