feat: move a config read at the pin with it

A profile following the branch tip (pin_follows) can carry a
config_reads entry read at the build a platform installs, which is
the pin itself: advmame's retropie entry reads advmame.rc at 96237a5.
bump_commit now advances such a revision with source_commit, and
leaves every other revision (another platform's build) alone.

scripts/profile_sync.py

@@ -3745,6 +3745,8 @@ def bump_commit(
     expected = dict(document)
     expected["source_commit"] = report.head
     new_text = _set_pin(text, document, "source_commit", report.head, "profiled_date")
+    if document.get("pin_follows"):
+        new_text, expected = _follow_config_reads(new_text, expected, document, report.head)
     if upstream_moves:
         expected["upstream_commit"] = report.upstream_head
         new_text = _set_pin(
@@ -3801,6 +3803,28 @@ def cites_primary(report: ProfileReport) -> bool:
     return not parts or any(part.repo is None for part in parts)
 
 
+def _follow_config_reads(
+    text: str, expected: dict, document: dict, head: str
+) -> tuple[str, dict]:
+    """A config_reads entry read at the pin moves with a pin that follows the
+    branch tip: RetroPie installs advmame from the tip, so the build its
+    advmame.rc is read at is the pin itself."""
+    pin = str(document.get("source_commit") or "")
+    reads = document.get("config_reads") or []
+    if not pin or not any(isinstance(r, dict) and r.get("revision") == pin for r in reads):
+        return text, expected
+    text = re.sub(
+        r'^(\s*revision:\s*)(["\']?)' + re.escape(pin) + r"\2\s*$",
+        lambda m: f"{m.group(1)}{m.group(2)}{head}{m.group(2)}",
+        text, flags=re.M,
+    )
+    expected = {**expected, "config_reads": [
+        {**r, "revision": head} if isinstance(r, dict) and r.get("revision") == pin else r
+        for r in reads
+    ]}
+    return text, expected
+
+
 def _set_pin(text: str, document: dict, field: str, value: str, after: str) -> str:
     """Write *field* as *value*, replacing its line or adding one after *after*."""
     current = document.get(field)

tests/test_profile_sync.py

@@ -3399,6 +3399,40 @@ class TestBumpCommit(unittest.TestCase):
         self.assertTrue(bump_commit(self.path, report))
         self.assertIn("newhead", self.path.read_text())
 
+    def test_a_config_read_at_the_pin_follows_it(self):
+        # RetroPie reads advmame.rc at the build it installs, the pin: the
+        # config_reads revision is the pin, and moves with it.
+        pin = "a" * 40
+        self.path.write_text(
+            SAMPLE.replace('profiled_date: "2026-03-29"\n',
+                           f'profiled_date: "2026-03-29"\nsource_commit: "{pin}"\n', 1)
+            + "built_by: [retropie]\n"
+            + 'pin_follows: "RetroPie builds the branch tip"\n'
+            + "config_reads:\n"
+            + '  - file: "advmame.rc"\n'
+            + "    platforms: [retropie]\n"
+            + f'    revision: "{pin}"\n'
+            + '    source_ref: "a.c:10-12"\n'
+            + "  - file: \"other.rc\"\n"
+            + "    platforms: [emuelec]\n"
+            + f'    revision: "{"b" * 40}"\n'
+            + '    source_ref: "a.c:10-12"\n',
+            encoding="utf-8",
+        )
+        part = PartResult(
+            RefPart("a.c", 10, 12, "a.c:10-12"), "ANCHORED", None, 10, 12, []
+        )
+        head = "c" * 40
+        report = ProfileReport(
+            name="p", repo="o/n", pin=pin, head=head,
+            entries=[EntryReport("a.bin", "a.c:10-12", "ANCHORED", [part])],
+            counts={"ANCHORED": 1},
+        )
+        self.assertTrue(bump_commit(self.path, report))
+        document = yaml.safe_load(self.path.read_text(encoding="utf-8"))
+        self.assertEqual(document["source_commit"], head)
+        self.assertEqual([r["revision"] for r in document["config_reads"]], [head, "b" * 40])
+
     def test_refused_when_no_ref_reads_the_pinned_repository(self):
         """gam4980: every bare libretro.c ref anchored in upstream, and the
         bump wrote the fork's HEAD over refs that never described it."""