encoding: per-slide pptx chunking + extract_blocks API; api: recency tiebreak

extract_blocks(filepath) is the new structured-extraction entry point, returning
list[{heading, text, kind}]. chunk_and_embed accepts either str (blind-chunk
back-compat) or list[dict] (one chunk per block, blind-split if oversize, heading
prepended for retrieval context and stored in metadata).

- pptx: one block per slide. Slide title becomes block heading; speaker notes
  fold into the body. Image-only decks with title-only slides now produce
  heading-only chunks instead of being recorded as extraction failures.
- docx: deliberately single-block (back-compat). Heading-style section detection
  was implemented and rolled back: hand-formatted CVs are Normal-styled with
  bold-as-heading, and tying chunk boundaries to formatting choices would lock
  future-user into preserving those choices forever. Lexical + cross-encoder
  retrieval already handles substring matching inside blind-chunked CVs.
- pdf/txt/md: unchanged (single block, blind chunking).

Recency tiebreak in retrieve_context: pull created_at into the SELECT, use it
as secondary sort key in _rerank so memory/journal snapshots prefer the latest
copy among near-duplicate content.

reindex_docx_pptx.py now accepts --ext=pptx,docx... so re-ingest can target a
subset; previous hardcoded delete regex would have wiped both even with a
single-ext target.

scripts/reindex_docx_pptx.py

@@ -12,6 +12,7 @@ Without --apply: dry-run. Counts files and chunks, prints a sample, writes nothi
 """
 
 import os
+import re
 import sys
 import time
 from pathlib import Path
@@ -28,19 +29,29 @@ sys.path.insert(0, str(Path(__file__).parent))
 from ingest import _ingest_one, get_pg
 
 NEXTCLOUD_PATH = Path("/home/aaron/nextcloud/data/data/aaron/files")
-TARGET_EXTS = {".docx", ".pptx"}
 
 APPLY = "--apply" in sys.argv
+_ext_args = [a for a in sys.argv[1:] if a.startswith("--ext=")]
+if _ext_args:
+    TARGET_EXTS = {("." + e.lstrip(".")) for arg in _ext_args
+                   for e in arg.split("=", 1)[1].split(",")}
+else:
+    TARGET_EXTS = {".docx", ".pptx"}
+
+
+def _ext_regex():
+    inner = "|".join(re.escape(e.lstrip(".")) for e in sorted(TARGET_EXTS))
+    return f"\\.({inner})$"
 
 
 def count_stale():
     pg = get_pg()
     cur = pg.cursor()
     cur.execute(
-        "SELECT lower(substring(source from '\\.[^.]+$')) AS ext, "
-        "COUNT(DISTINCT source) AS files, COUNT(*) AS chunks "
-        "FROM embeddings WHERE lower(source) ~ '\\.(docx|pptx)$' "
-        "GROUP BY 1 ORDER BY 1"
+        f"SELECT lower(substring(source from '\\.[^.]+$')) AS ext, "
+        f"COUNT(DISTINCT source) AS files, COUNT(*) AS chunks "
+        f"FROM embeddings WHERE lower(source) ~ '{_ext_regex()}' "
+        f"GROUP BY 1 ORDER BY 1"
     )
     rows = cur.fetchall()
     pg.close()
@@ -50,7 +61,7 @@ def count_stale():
 def delete_stale():
     pg = get_pg()
     cur = pg.cursor()
-    cur.execute("DELETE FROM embeddings WHERE lower(source) ~ '\\.(docx|pptx)$'")
+    cur.execute(f"DELETE FROM embeddings WHERE lower(source) ~ '{_ext_regex()}'")
     deleted = cur.rowcount
     pg.commit()
     pg.close()