fix: save hook auto-mines transcript without MEMPAL_DIR (#840)

TDD: test written first, failed, then fixed.

Problem: save hook says "saved in background" but MEMPAL_DIR defaults
to empty, so nothing actually mines. Users get no auto-save despite
the hook firing every 15 messages.

Fix: use TRANSCRIPT_PATH (received from Claude Code in the hook's
JSON input) to discover the session directory. Mine that directory
automatically. MEMPAL_DIR is still supported as override but no
longer required.

Also fixed: bare python3 → $(command -v python3) for nohup safety.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

hooks/mempal_save_hook.sh

@@ -133,11 +133,20 @@ if [ "$SINCE_LAST" -ge "$SAVE_INTERVAL" ] && [ "$EXCHANGE_COUNT" -gt 0 ]; then
 
     echo "[$(date '+%H:%M:%S')] TRIGGERING SAVE at exchange $EXCHANGE_COUNT" >> "$STATE_DIR/hook.log"
 
-    # Optional: run mempalace ingest in background if MEMPAL_DIR is set
+    # Auto-mine the transcript. Two paths:
+    # 1. TRANSCRIPT_PATH (from Claude Code) — mine the directory it lives in
+    # 2. MEMPAL_DIR (user-configured) — mine that directory
+    # At least one should work. If neither is set, nothing mines.
+    PYTHON="$(command -v python3)"
+    MINE_DIR=""
+    if [ -n "$TRANSCRIPT_PATH" ] && [ -f "$TRANSCRIPT_PATH" ]; then
+        MINE_DIR="$(dirname "$TRANSCRIPT_PATH")"
+    fi
     if [ -n "$MEMPAL_DIR" ] && [ -d "$MEMPAL_DIR" ]; then
-        SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
-        REPO_DIR="$(dirname "$SCRIPT_DIR")"
-        python3 -m mempalace mine "$MEMPAL_DIR" >> "$STATE_DIR/hook.log" 2>&1 &
+        MINE_DIR="$MEMPAL_DIR"
+    fi
+    if [ -n "$MINE_DIR" ]; then
+        "$PYTHON" -m mempalace mine "$MINE_DIR" >> "$STATE_DIR/hook.log" 2>&1 &
     fi
 
     # Notify the AI that a checkpoint happened — but do NOT ask it to write

tests/test_save_hook_mines.py

@@ -0,0 +1,68 @@
+"""TDD: save hook must actually mine conversations without MEMPAL_DIR.
+
+The save hook should auto-discover the conversation transcript and mine it
+without the user needing to set MEMPAL_DIR. Currently MEMPAL_DIR defaults
+to empty, which means the mining block is skipped and nothing is saved
+despite the hook telling the agent "saved in background."
+
+Written BEFORE the fix.
+"""
+
+import os
+
+
+class TestSaveHookAutoMines:
+    """The save hook must mine the active transcript automatically."""
+
+    def test_hook_mines_transcript_path(self):
+        """The hook receives TRANSCRIPT_PATH from Claude Code.
+        It should use that to mine the conversation, not depend on MEMPAL_DIR."""
+        hook_path = os.path.join(
+            os.path.dirname(os.path.dirname(__file__)),
+            "hooks",
+            "mempal_save_hook.sh",
+        )
+        src = open(hook_path).read()
+
+        # The hook ALREADY receives TRANSCRIPT_PATH in the JSON input.
+        # It should use this to mine the current session's transcript
+        # regardless of whether MEMPAL_DIR is set.
+        # The hook must have a path that uses TRANSCRIPT_PATH to determine
+        # what to mine, separate from the MEMPAL_DIR path.
+        uses_transcript = "TRANSCRIPT_PATH" in src
+        has_mine = "mempalace mine" in src
+        # TRANSCRIPT_PATH must appear in the mining logic, not just the parse block
+        transcript_drives_mine = "MINE_DIR" in src and "dirname" in src and "TRANSCRIPT_PATH" in src
+
+        assert uses_transcript and has_mine and transcript_drives_mine, (
+            "Save hook only mines when MEMPAL_DIR is set (defaults to empty). "
+            "The hook receives TRANSCRIPT_PATH from Claude Code — it should "
+            "mine that file automatically so conversations are saved without "
+            "the user setting an env var. Currently the hook says 'saved in "
+            "background' but nothing actually saves."
+        )
+
+    def test_mempal_dir_default_not_empty(self):
+        """If MEMPAL_DIR is still used, it should have a sensible default,
+        not an empty string that silently disables mining."""
+        hook_path = os.path.join(
+            os.path.dirname(os.path.dirname(__file__)),
+            "hooks",
+            "mempal_save_hook.sh",
+        )
+        src = open(hook_path).read()
+
+        # Check if MEMPAL_DIR defaults to empty
+        has_empty_default = 'MEMPAL_DIR=""' in src
+
+        # If it defaults to empty, mining is silently disabled
+        if has_empty_default:
+            # There must be an alternative mining path that doesn't need MEMPAL_DIR
+            has_alternative = (
+                src.count("mempalace mine") > 1
+                or "TRANSCRIPT_PATH" in src.split("mempalace mine")[0]
+            )
+            assert has_alternative, (
+                'MEMPAL_DIR defaults to "" which silently disables mining. '
+                "Either set a default path or add transcript-based mining."
+            )