Address Copilot review: cursor tie-break, honest metrics, accurate comments

Six items from the automated review on PR #998:

1. **Cursor tie-break bug (correctness).** The skip condition was
   `rec.timestamp <= cursor`; if multiple messages share the max
   timestamp and only some were ingested before a crash, the rest
   would be lost forever. Changed to `< cursor`, relying on
   deterministic drawer IDs for safe re-attempt at the boundary.
   Regression test
   `test_sweep_recovers_untaken_message_at_cursor_timestamp`.

2. **`drawers_added` counted upserts, not adds.** Added a pre-flight
   `collection.get(ids=batch)` to distinguish new rows from already-
   present ones. Return value now carries `drawers_added`,
   `drawers_already_present`, `drawers_upserted`, and `drawers_skipped`
   separately. Dict-compatible access (`existing.get("ids")`) keeps it
   working on both the raw Chroma return and the typed `GetResult`.

3. **`sweep_directory` hid failures in the summary.** `files_processed`
   used to exclude failed files. Replaced with `files_attempted` (all
   discovered) + `files_succeeded` (subset that completed); CLI output
   shows `succeeded/attempted`.

4. **Coordination claim was overstated.** The primary miners don't
   stamp `session_id`/`timestamp` metadata, so the sweeper coordinates
   only with its own prior runs. Softened docstrings on module and CLI
   command. Uniform cross-miner metadata is flagged as a follow-up.

5. **MAX_FILE_SIZE comments were misleading.** Said source size "does
   not affect storage or embedding cost" — true per-drawer, but source
   size still scales drawer count, embedding work, and memory usage
   (files are read in full, not streamed). Corrected in both
   `miner.py` and `convo_miner.py`.

6. Added the tie-break regression test that reproduces the correctness
   bug from (1).

Tests: 970 passed (was 969), ruff + pre-commit clean.

Co-Authored-By: MSL <232237854+milla-jovovich@users.noreply.github.com>

mempalace/convo_miner.py

@@ -58,8 +58,11 @@ CHUNK_SIZE = 800  # chars per drawer — align with miner.py
 MAX_FILE_SIZE = 500 * 1024 * 1024  # 500 MB — skip files larger than this.
 # Matches miner.py at 500 MB. Long Claude Code sessions, multi-year
 # ChatGPT exports, and lifetime Slack dumps routinely exceed 10 MB; the
-# cap at that level silently dropped them with `continue`. Source size
-# does not affect storage or embedding cost — chunking happens downstream.
+# cap at that level silently dropped them with `continue`. Per-drawer
+# size is bounded by CHUNK_SIZE, but larger source files still produce
+# more drawers and therefore more embedding/storage work — and content
+# is normalized and loaded fully into memory before chunking, so memory
+# use also scales with source size.
 
 
 def _register_file(collection, source_file: str, wing: str, agent: str):