fix(1d): custom-html backup/restore overlay reads marker via exec (volume-direct)

http_fetch raced the serving layer right after backup-bot cycled the app container (served '' for a
moment). Backup/restore preserve the VOLUME, so read the marker in-container via exec_in_app — correct
and race-free. Serving is proven separately by install/upgrade assert_serving.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/custom-html/test_backup.py

@@ -1,6 +1,11 @@
 """custom-html — BACKUP overlay (Phase 1d, DG4): seed a known state, back it up (assert artifact),
 then mutate so the RESTORE overlay (test_restore.py) can prove the backed-up state returns. Runs on
-the shared deployment; the marker it leaves ("mutated") persists for the restore tier."""
+the shared deployment; the marker it leaves ("mutated") persists for the restore tier.
+
+Reads the marker via `exec_in_app` (the file in the volume), NOT http: backup/restore preserve the
+VOLUME, and reading it directly is immune to the serving/container-routing race right after
+backup-bot-two cycles the app container (HTTP briefly served empty). Serving is proven separately by
+the install/upgrade tiers' assert_serving."""
 
 import os
 import sys
@@ -11,15 +16,19 @@ from harness import generic, lifecycle  # noqa: E402
 MARKER_PATH = "/usr/share/nginx/html/ci-marker.txt"
 
 
+def _marker(domain: str) -> str:
+    return lifecycle.exec_in_app(domain, ["cat", MARKER_PATH]).strip()
+
+
 def test_backup_captures_state(live_app, meta):
     domain = live_app
-    # 1) establish a known original state, then back it up (reuse the generic op: backup + assert
+    # 1) establish a known original state, then back it up (reuse the generic op: backup + assert a
-    #    a snapshot artifact was produced)
+    #    snapshot artifact was produced)
     lifecycle.exec_in_app(domain, ["sh", "-c", f"echo original > {MARKER_PATH}"])
-    assert lifecycle.http_fetch(domain, "/ci-marker.txt")[1].strip() == "original"
+    assert _marker(domain) == "original"
     snap = generic.do_backup(domain)
     assert snap, "backup produced no snapshot artifact"
 
     # 2) mutate state so a successful restore is observable (diverge from the backup)
     lifecycle.exec_in_app(domain, ["sh", "-c", f"echo mutated > {MARKER_PATH}"])
-    assert lifecycle.http_fetch(domain, "/ci-marker.txt")[1].strip() == "mutated"
+    assert _marker(domain) == "mutated"

tests/custom-html/test_restore.py

@@ -3,8 +3,9 @@
 Runs after the backup overlay (test_backup.py) on the SAME shared deployment, which left state
 mutated to "mutated" after backing up "original". This restores the snapshot via the shared op
 helper (`generic.do_restore`, which also asserts the app is healthy + serving afterwards), then
-asserts the served data returned to the pre-mutation "original" — the app-specific data integrity the
+asserts the VOLUME data returned to the pre-mutation "original" — the app-specific data integrity the
-generic restore cannot check. Assertion-only (no deploy/teardown)."""
+generic restore cannot check. Reads the marker via exec_in_app (volume-direct, robust to the
+post-restore serving race). Assertion-only (no deploy/teardown)."""
 
 import os
 import sys
@@ -12,10 +13,13 @@ import sys
 sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "..", "runner"))
 from harness import generic, lifecycle  # noqa: E402
 
+MARKER_PATH = "/usr/share/nginx/html/ci-marker.txt"
+
 
 def test_restore_returns_state(live_app, meta):
     domain = live_app
     generic.do_restore(domain, meta)  # restore + assert healthy/serving
+    restored = lifecycle.exec_in_app(domain, ["cat", MARKER_PATH]).strip()
     assert (
-        lifecycle.http_fetch(domain, "/ci-marker.txt")[1].strip() == "original"
+        restored == "original"
-    ), "restore did not return the pre-mutation (backed-up) state"
+    ), f"restore did not return the pre-mutation (backed-up) state: got {restored!r}"