fix(diary): detect same-size edits via content hash

The skip-if-unchanged check compared byte length only, so any in-place
edit preserving total length (typo fix "teh"→"the", word swap) was
silently dropped — a verbatim-storage violation: the user's actual
words never reached the palace.

Switch the gate to sha256(text). State entries gain a "content_hash"
field; the legacy size-only path is preserved when prev_hash is missing
so a post-upgrade run does not re-ingest every untouched diary.

Closes #925

mempalace/diary_ingest.py

@@ -120,12 +120,22 @@ def ingest_diaries(
             continue
         date_str = date_match.group(1)
 
-        # Skip if content hasn't changed
+        # Skip if content hasn't changed. Hash-based — size alone false-negatives
+        # on same-length edits (e.g. "teh" → "the"), silently dropping real edits.
         state_key = f"{wing}|{diary_path.name}"
-        prev_size = state.get(state_key, {}).get("size", 0)
+        prev_entry = state.get(state_key, {})
+        prev_hash = prev_entry.get("content_hash")
+        prev_size = prev_entry.get("size", 0)
         curr_size = len(text)
-        if curr_size == prev_size and not force:
-            continue
+        curr_hash = hashlib.sha256(text.encode("utf-8")).hexdigest()
+        if not force:
+            if prev_hash is not None:
+                if curr_hash == prev_hash:
+                    continue
+            elif curr_size == prev_size and prev_size > 0:
+                # Legacy state without content_hash: keep size-based skip so a
+                # post-upgrade run doesn't re-ingest every untouched diary.
+                continue
 
         now_iso = datetime.now(timezone.utc).isoformat()
         drawer_id = _diary_drawer_id(wing, date_str)
@@ -184,6 +194,7 @@ def ingest_diaries(
 
             state[state_key] = {
                 "size": curr_size,
+                "content_hash": curr_hash,
                 "entry_count": len(entries),
                 "ingested_at": now_iso,
             }