fix(slice4): make all entry write paths sidecar-aware (§22.4a carried from SLICE-1)

graduate, claim, retire/unretire, _read_meta_entry, mark_entry_reviewed,
body extract/wrap (api_branches + api_prs replay) now dual-read and write
metadata to the sidecar via write_entry_files + bot.commit_entry_files/
open_entry_pr — a migrated body-only .md no longer crashes entry.parse or
re-grows frontmatter; legacy entries lazy-migrate on first metadata write.
Existing tests updated to assert the sidecar (INV-2 clean docs).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/tests/test_graduation_vertical.py

@@ -48,6 +48,18 @@ PITCH = (
 )
 
 
+def _entry_from_git(fake, slug, branch="main"):
+    """§22.4a SLICE-4: read an entry's combined metadata+body from git via the
+    dual-read parser — graduation/claim now write metadata to the sidecar and
+    keep the body in the `.md`, so an Entry is reconstructed from both."""
+    from app import metadata
+    md = fake.files[("wiggleverse", "meta", branch, f"rfcs/{slug}.md")]["content"]
+    sc = fake.files.get(
+        ("wiggleverse", "meta", branch, f"rfcs/{slug}.meta.yaml"), {}).get("content")
+    e, _ = metadata.read_entry(md, sc, fallback_slug=slug)
+    return e
+
+
 def seed_owned_super_draft(fake: FakeGitea, *, slug: str, title: str, pitch: str,
                             owners: list[str], arbiters: list[str] | None = None,
                             proposed_by: str = "alice", tags: list[str] | None = None) -> None:
@@ -190,9 +202,8 @@ def test_graduate_happy_path_flips_in_place_keeping_body(app_with_fake_gitea):
             k[1].startswith("rfc-0042") for k in fake.repos
         ), f"a per-RFC repo was created: {fake.repos}"
 
-        # Meta entry on main: state flipped, body KEPT, repo null.
-        meta_text = fake.files[("wiggleverse", "meta", "main", "rfcs/ohm.md")]["content"]
-        graduated = entry_mod.parse(meta_text)
+        # Meta entry on main: state flipped (sidecar), body KEPT (.md), repo null.
+        graduated = _entry_from_git(fake, "ohm")
         assert graduated.state == "active"
         assert graduated.id == "RFC-0042"
         assert graduated.repo is None
@@ -247,7 +258,7 @@ def test_graduate_preserves_unknown_frontmatter_keys(app_with_fake_gitea):
                         json={"rfc_id": "RFC-0042", "owners": ["ben"]})
         assert r.status_code == 200, r.text
 
-        graduated = entry_mod.parse(fake.files[key]["content"])
+        graduated = _entry_from_git(fake, "ohm")
         assert graduated.state == "active"
         assert graduated.extra.get("priority") == "P1"
 
@@ -599,8 +610,7 @@ def test_graduate_without_number_flips_to_active_null_id_by_slug(app_with_fake_g
         assert d["rfc_id"] is None
 
         # Meta entry: active, id null, body kept, graduation stamped.
-        meta_text = fake.files[("wiggleverse", "meta", "main", "rfcs/ohm.md")]["content"]
-        graduated = entry_mod.parse(meta_text)
+        graduated = _entry_from_git(fake, "ohm")
         assert graduated.state == "active"
         assert graduated.id is None
         assert graduated.graduated_by == "ben"
@@ -649,9 +659,7 @@ def test_graduate_with_number_unchanged_when_id_absent_field(app_with_fake_gitea
         r = client.post("/api/rfcs/ohm/graduate?_sync=1", json={"owners": ["ben"]})
         assert r.status_code == 200, r.text
         assert r.json()["rfc_id"] is None
-        graduated = entry_mod.parse(
-            fake.files[("wiggleverse", "meta", "main", "rfcs/ohm.md")]["content"]
-        )
+        graduated = _entry_from_git(fake, "ohm")
         assert graduated.state == "active"
         assert graduated.id is None
 
@@ -677,8 +685,7 @@ def test_claim_opens_meta_pr(app_with_fake_gitea):
         d = r.json()
         assert d["branch_name"] == "claim/ohm"
 
-        text = fake.files[("wiggleverse", "meta", "claim/ohm", "rfcs/ohm.md")]["content"]
-        ent = entry_mod.parse(text)
+        ent = _entry_from_git(fake, "ohm", branch="claim/ohm")
         assert "alice" in ent.owners
 
         row = db.conn().execute(