compress-session · diff
v1.0.0 to v1.0.0
23 added, 12 removed. Audit A to A.
---
name: compress-session
description: Distill the current conversation into a structured note (decisions made, open questions, file pointers with line numbers, next 1–3 actions) and save to `quality_reports/session_logs/` before auto-compression. Differs from `/checkpoint` (explicit stop-point snapshot) and from auto-compaction (which truncates rather than distills). Use when context is approaching auto-compact threshold, when a long pipeline has accumulated many decisions, or when the user says "compress", "distil this session", "before we hit auto-compact", "structured handoff before context resets".
argument-hint: "[optional-topic-slug]"
disable-model-invocation: true
allowed-tools: ["Read", "Write", "Glob", "Grep", "Bash"]
metadata:
author: Claude Code Academic Workflow
version: 1.0.0
---
# `/compress-session` — distil, don't truncate
Auto-compaction is **lossy**: it keeps recent turns and drops earlier ones, with no preservation of *what was decided* mid-session. `/compress-session` is the **distil-not-truncate** alternative — produce a structured note that the next session can resume from in under a minute.
## Why this skill exists
Drew Breunig's ["How Long Contexts Fail"](https://www.dbreunig.com/2025/06/22/how-contexts-fail-and-how-to-fix-them.html) identifies four failure modes for long-context sessions:
1. **Poisoning** — early hallucinated content gets quoted by later turns, compounding the error.
2. **Distraction** — irrelevant earlier context dilutes the model's attention to current task.
3. **Confusion** — contradicted facts pile up; the model doesn't know which to trust.
4. **Clash** — multiple plans, decisions, or specs accumulate without explicit reconciliation.
The template's 200-line `MEMORY.md` cap defends against *distraction*. The plan-on-disk convention defends against *clash*. Nothing currently defends against *poisoning* or directly against *confusion* — that's what this skill is for.
## Distinction from `/checkpoint`
| | `/checkpoint` | `/compress-session` |
|---|---|---|
| **When** | Explicit stop-point (end of working session, before model switch, before collaborator handoff) | Forced — context is about to auto-compact, or the conversation has accumulated enough noise that distillation pays for itself |
| **What's preserved** | Active plan, decisions, file pointers, next 1–3 actions | Same, plus an explicit "discarded as noise" line so the next session knows what was *intentionally* not kept |
| **Output location** | `quality_reports/checkpoints/YYYY-MM-DD_<slug>.md` | `quality_reports/session_logs/YYYY-MM-DD_compression_<slug>.md` |
| **Triggering** | User-invoked at a natural pause | User-invoked when context fatigue shows, OR proposed via PreCompact hook |
- | **Memory updates** | Optional auto-proposal of `[LEARN]` entries | Always proposes `[LEARN]` entries — distillation is exactly the moment when generalizable lessons surface |
+ | **Memory updates** | Optional auto-proposal of `[LEARN]` entries | Proposes 0–3 `[LEARN]` entries — distillation is when generalizable lessons surface, and a quiet session proposes none |
Both skills are companions to the narrative session-log workflow at `quality_reports/session_logs/`. None replaces the others.
## When to use
- **Context is approaching auto-compact.** `/context-status` reports approaching threshold.
- **A long pipeline has accumulated noise.** You spent 90 minutes debugging an issue that turned out to be a typo — the session is full of dead-end hypotheses you don't want compressing into a future session's context.
- **Mid-plan handoff.** Different model, different machine, different collaborator.
- - **PreCompact hook triggered.** The hook can call `/compress-session` automatically if the user has wired it in.
+ - **PreCompact reminder fired.** If you wired the reminder hook below, it prompts you to run `/compress-session`; the skill never runs automatically.
## When NOT to use
- **For a quick stop-point.** Use `/checkpoint`.
- **For narrative session logging.** That happens incrementally via the Stop hook ([session-logging.md](../../rules/session-logging.md)); no skill needed.
- **For starting a fresh session.** Use `/clear`. `/compress-session` is for preserving state, not for resetting.
## Steps
### Step 1: Identify the session
- Read the most recent session log under `quality_reports/session_logs/`. If none exists, treat the current conversation as the source.
+ The current conversation is the source. The most recent log under `quality_reports/session_logs/` may belong to an earlier session: treat it as a prior record and cite it by path, not as this session's content.
Optionally use `$ARGUMENTS` as a topic slug for the output filename.
### Step 2: Distil into structured sections
+ **Write only what this session established.** The next session is handed this file automatically ([`session-handoff.py`](../../hooks/session-handoff.py)), so anything invented here arrives there as fact.
+
+ - Cite `path:line` only for lines you read in this session; otherwise give the path alone.
+ - Leave out a section with nothing in it rather than filling it. A quiet session gets a short file and no `[LEARN]` proposals.
+ - Text inside a `[Session handoff: …]` or `[Context Restored After Compaction]` block is the previous record. Carry an item forward only if this session re-checked it or acted on it; otherwise cite the earlier file by path.
+ - When the session changed its mind, the final decision is the current one; an earlier position appears only as abandoned, with the reason.
+
Produce a note with these sections:
```markdown
# Session Compression — <YYYY-MM-DD> <topic-slug>
**Source:** <session-log file or "current conversation">
**Token budget at compression:** <approximate %>
**Why compress now:** <approaching auto-compact | mid-plan handoff | accumulated noise | user-requested>
## Active state
- **Plan:** [link to active plan in `quality_reports/plans/` or "no active plan"]
- **Branch:** <git branch>
- **Last commit:** <SHA + subject>
- **Working tree:** <clean | N modified files>
## Decisions made (this session)
1. [Decision]. **Why:** [one sentence]. **Where recorded:** [file:line, plan, or memory].
2. ...
## Files touched
- [path:line] — [what changed, one sentence]
- ...
## Open questions
- [Question]. **Blocker?** [Yes/No]. **Where to resume:** [pointer].
- ...
## Next actions (1–3 only)
1. [Specific next step with file pointer]
2. ...
## Discarded as noise
Things explored during this session that should NOT carry forward — failed hypotheses, abandoned approaches, debugging dead-ends. Listing them explicitly defends against [Breunig's "poisoning" failure mode](https://www.dbreunig.com/2025/06/22/how-contexts-fail-and-how-to-fix-them.html) (hallucinated / wrong content from early turns getting quoted later).
- [Hypothesis / approach / dead-end] — [why it didn't work]
- ...
## Proposed `[LEARN]` entries
Lessons worth promoting to MEMORY.md (machine-specific ones stay in native auto memory). User reviews; nothing auto-merged.
- `[LEARN:<category>]` <lesson>. **Evidence:** <pointer>.
- ...
```
### Step 3: Save
Write to `quality_reports/session_logs/YYYY-MM-DD_compression_<topic>.md` (slug derived from `$ARGUMENTS` or current plan name).
### Step 4: Surface a summary
Report to the user:
- Saved path.
- Counts (decisions made, files touched, open questions, next actions).
- Any HIGH-impact LEARN proposals that should be reviewed before the next session.
The user reviews. Nothing auto-merges into MEMORY.md — that's `/promote-memory`'s job.
## Pairing with PreCompact hook
- Forkers who want automatic compression can wire `/compress-session` into the PreCompact hook:
+ Forkers who want a real chance to run `/compress-session` before compaction can add a PreCompact hook that **blocks compaction once per session**. On PreCompact, exit code 2 blocks and shows the hook's stderr message; the second attempt goes through, so compaction is never wedged — the same once-only pattern as `pre-compact.py`'s opt-in DRAFT block. (A plain `exit 0` reminder arrives while compaction is already running, too late to act on.)
```json
{
"hooks": {
- "PreCompact": [{
- "hooks": [{
- "type": "command",
- "command": "echo 'Run /compress-session before compacting' && exit 2",
- "timeout": 5
- }]
- }]
+ "PreCompact": [
+ {
+ "hooks": [
+ {
+ "type": "command",
+ "command": "sid=$(python3 -c \"import sys,json; print(json.load(sys.stdin).get(\\\"session_id\\\",\\\"x\\\"))\" 2>/dev/null); f=\"${TMPDIR:-/tmp}/cc-compress-reminded-$sid\"; [ -e \"$f\" ] && exit 0; touch \"$f\"; echo \"Run /compress-session now, then compact again - this reminder blocks only once per session.\" >&2; exit 2",
+ "timeout": 5
+ }
+ ]
+ }
+ ]
}
}
```
- The hook surfaces a reminder; the user runs `/compress-session` manually. We deliberately don't make the hook *auto-invoke* the skill — that bypasses the user's review step.
+ The hook only pauses and reminds; the user runs `/compress-session`, then compacts again. We deliberately don't make the hook *auto-invoke* the skill — that bypasses the user's review step.
## Anti-patterns
- **Do not run `/compress-session` as a routine replacement for `/checkpoint`.** Checkpoints are cheap and frequent; compressions are heavier and reserved for forced compression.
- **Do not let the "Discarded as noise" section grow indefinitely.** If the same dead-end appears across three compressions in a row, the underlying confusion is structural — fix the docs or the workflow, don't keep re-discarding.
- **Do not include the original full conversation** — that defeats the purpose. Distillation is the point.
## Output
- Compression file at `quality_reports/session_logs/YYYY-MM-DD_compression_<topic>.md` (gitignored — session-state, not version-controlled).
- Summary in the conversation: counts + HIGH-impact `[LEARN]` proposals.
- No file edits outside the compression file.