Add transcript backup tracking system and pre-compact hook improvements

- pre-compact-backup.sh: derive transcript path from session_id+cwd (no
  longer relies on transcript_path field that Claude Code stopped providing);
  register each backup in tracking.json after saving
- extract-transcripts.py: new script managing tracking.json — register,
  list, extract conversation text, mark-processed modes
- list-transcripts-here.sh: thin wrapper for extract-transcripts --list
  using $(pwd); needed because SKILL.md bang commands reject $() substitution
- install-hooks.sh: now also symlinks skill-helper scripts into
  ~/.claude/scripts/ via a curated SKILL_HELPERS list
- Memory docs: new script-extract-transcripts.md, script-list-transcripts-here.md;
  updated skill-log.md, script-install-hooks.md, MEMORY.md index

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

memory/script-extract-transcripts.md

@@ -0,0 +1,41 @@
+# script: extract-transcripts
+
+**Location:** `claude-foundations/scripts/extract-transcripts.py`  
+**Symlinked to:** `~/.claude/scripts/extract-transcripts.py`
+
+## Purpose
+
+Manages the transcript backup tracking system. Registers pre-compaction JSONL backups, lists unprocessed ones per project, extracts readable conversation text for analysis, and marks entries as processed after a log is written.
+
+## Usage
+
+```bash
+# Register a new backup (called by pre-compact-backup.sh hook)
+python3 ~/.claude/scripts/extract-transcripts.py \
+  --register BACKUP_NAME --session-id SESSION_ID --cwd PROJECT_CWD
+
+# List unprocessed transcripts for a project (used by /log skill)
+python3 ~/.claude/scripts/extract-transcripts.py --list /home/paul/dev/claude/projects/foo
+# → compact JSON array of {backup, session_id, saved_at, path, exists}
+
+# Extract readable conversation from one backup (used by /log Sonnet subagent)
+python3 ~/.claude/scripts/extract-transcripts.py --extract BACKUP_NAME
+
+# Mark all unprocessed backups for a project as done
+python3 ~/.claude/scripts/extract-transcripts.py \
+  --mark-all-processed /home/paul/dev/claude/projects/foo --log-file memory/log/YYYY-MM-DD.HHMMSS-transcripts.md
+```
+
+## How it works
+
+- Tracking state lives in `~/.claude/transcript-backups/tracking.json`, keyed by backup filename
+- Each entry: `{session_id, cwd, saved_at, processed, log_file, processed_at}`
+- `--list` filters by `cwd == project_cwd` and `processed == false` — output is metadata only (no content), safe for skill pre-gathering
+- `--extract` reads the JSONL, skips sidechain entries, extracts `user`/`assistant` message text, truncates per-message at 3000 chars
+- Tool use blocks are summarised as `[tool: ToolName(key=...)]` rather than shown in full
+
+## Gotchas
+
+- `sys.exit(0)` inside a bare `except: pass` block is caught as SystemExit — always use specific exception types or `break` when early exit is needed inside exception handlers
+- The JSONL entries for `type: "user"` without a `message` field (e.g., file-history snapshots) are skipped silently
+- Old backups with `-auto` suffix (from before this system) are not in tracking.json and will never appear in `--list`