End-of-session: transcript tracking log, context update, README docs

- Add session log (2026-04-13) covering transcript backup tracking system
- Add context/transcript-tracking.md: first-run verification checklist for
  the Sonnet subagent path in /log
- Update CONTEXT.md with transcript tracking entry
- Update README.md: document extract-transcripts.py and list-transcripts-here.sh;
  note that install-hooks.sh now covers skill-helper scripts too
- Prune 3 reflected logs older than retention_days (7): 2026-03-23, -25, -29

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

context/transcript-tracking.md

@@ -0,0 +1,28 @@
+# Transcript Tracking System — Pending Verification
+
+## Status
+Built and committed (2026-04-13, commit `6fd0dac`). Pending first real-run verification.
+
+## What was built
+- `pre-compact-backup.sh` — fixed to derive transcript path from `session_id+cwd`; now registers each backup in `~/.claude/transcript-backups/tracking.json`
+- `extract-transcripts.py` — manages tracking.json; modes: `--register`, `--list`, `--extract`, `--mark-all-processed`
+- `list-transcripts-here.sh` — wrapper for `--list $(pwd)` (needed because SKILL.md bang commands reject `$()` substitution)
+- `/log` skill (in custom-claude-skills) — spawns Sonnet subagent to read JSONL backups and write `HHMMSS-transcripts.md` companion log
+
+## What to verify on first real run
+
+When `/log` is run in a session where context compression fired at least once:
+
+1. Check `~/.claude/transcript-backups/tracking.json` has an entry for the session with `processed: false`
+2. Run `/log` — it should show unprocessed transcripts in the pre-gathered metadata
+3. The Sonnet subagent should write `memory/log/YYYY-MM-DD.HHMMSS-transcripts.md` in the **project directory** (absolute path)
+4. After `/log` completes, `tracking.json` entry should show `processed: true` with a `log_file` path
+
+**Known risk:** The subagent prompt template asks it to write to `[PROJECT_ABS_PATH]/memory/log/...` — if it uses a relative path from the wrong cwd, the file lands in the wrong place. If that happens, update the subagent prompt in `/log` SKILL.md to include an explicit `cd [CWD]` instruction.
+
+## Files
+- Hook: `~/dev/claude/projects/claude-foundations/hooks/pre-compact-backup.sh`
+- Scripts: `~/dev/claude/projects/claude-foundations/scripts/extract-transcripts.py` and `list-transcripts-here.sh`
+- Symlinked to: `~/.claude/scripts/`
+- Skill: `~/dev/claude/projects/custom-claude-skills/skills/log/SKILL.md`
+- Tracking state: `~/.claude/transcript-backups/tracking.json`