design: compression eval harness — add three scrubbed fixtures + scrubber

Adds scripts/compression_eval/ with a design doc, README, a placeholder
run_eval.py, and three checked-in scrubbed session fixtures. No working
eval yet — PR is for design review before implementation.

Motivation: we edit agent/context_compressor.py prompts and
_template_sections by hand and ship without any automated check that
compression still preserves file paths, error codes, or the active task.
Factory.ai's Dec 2025 write-up
(https://factory.ai/news/evaluating-compression) documents a probe-based
eval scored on six dimensions. We adopt the methodology; we do not publish
scores.

Contents:
- DESIGN.md — fixture format, probe format (recall / artifact /
  continuation / decision), six grading dimensions, report format,
  cost expectations, scrubber pipeline, open questions, and staged
  follow-up PR plan.
- README.md — short 'what this is / when to run it' page.
- run_eval.py — placeholder that prints 'not implemented, see
  DESIGN.md' and exits 1.
- scrub_fixtures.py — reproducible pipeline that converts real sessions
  from ~/.hermes/sessions/*.jsonl into public-safe JSON fixtures.
  Applies: redact_sensitive_text, username path normalization, personal
  handle scrubbing, email and git-author normalization, reasoning
  scratchpad / <think> stripping, platform user-mention scrubbing,
  first-user paraphrase, system-prompt placeholder, orphan-message
  pruning, and tool-output size truncation for fixture readability.
- fixtures/feature-impl-context-priority.json — 75 msgs / ~17k tokens.
  Investigate → patch → test → PR → merge.
- fixtures/debug-session-feishu-id-model.json — 59 msgs / ~13k tokens.
  PR triage + upstream docs + decision.
- fixtures/config-build-competitive-scouts.json — 61 msgs / ~23k tokens.
  Iterative config accumulation (11 cron jobs across 7 weekdays).

PII audit: zero matches across the three fixtures for the maintainer's
handle (all case variants), personal email domains, and known contributor
emails. Only 'contributor@example.com' placeholder remains.

Why scripts/: requires API credentials, costs ~\$1 per run, LLM-graded
(non-deterministic), must not run in CI. scripts/sample_and_compress.py
is the existing precedent for offline credentialed tooling.
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# Compression Eval — Design
Status: proposal. Nothing under `scripts/compression_eval/` runs in CI.
This is an offline tool authors run before merging prompt or algorithm
changes to `agent/context_compressor.py`.
## Why
We tune the compressor prompt and the `_template_sections` checklist by
hand, ship, and wait for the next real session to notice regressions.
There is no automated check that a prompt edit still preserves file
paths, error messages, or the active task across a compression.
Factory.ai's December 2025 write-up
(https://factory.ai/news/evaluating-compression) describes a
probe-based eval that scores compressed state on six dimensions. The
methodology is the valuable part — the benchmarks in the post are a
marketing piece. We adopt the methodology and discard the scoreboard.
## Goal
Given a real session transcript and a bank of probe questions that
exercise what the transcript contained, answer:
1. After `ContextCompressor.compress()` runs, can the agent still
answer each probe correctly from the compressed state?
2. Which of the six dimensions (accuracy, context awareness, artifact
trail, completeness, continuity, instruction following) is the
prompt weakest on?
3. Does a prompt change improve or regress any dimension vs. the
previous run?
That is the full scope. No "compare against OpenAI and Anthropic"
benchmarking, no public scoreboard, no marketing claims.
## Non-goals
- Not a pytest. Requires API credentials, costs money, takes minutes
per fixture, and output is LLM-graded and non-deterministic.
- Not part of `scripts/run_tests.sh`. Not invoked by CI.
- Not a replacement for the existing compressor unit tests in
`tests/agent/test_context_compressor.py` — those stay as the
structural / boundary / tool-pair-sanitization guard.
- Not a general trajectory eval. Scoped to context compaction only.
## Where it lives
```
scripts/compression_eval/
├── DESIGN.md # this file
├── README.md # how to run, cost expectations, caveats
├── run_eval.py # entry point (fire CLI, like sample_and_compress.py)
├── scrub_fixtures.py # regenerate fixtures from ~/.hermes/sessions/*.jsonl
├── fixtures/ # checked-in scrubbed session snapshots
│ ├── feature-impl-context-priority.json
│ ├── debug-session-feishu-id-model.json
│ └── config-build-competitive-scouts.json
├── probes/ # probe banks paired with fixtures
│ └── <fixture>.probes.json
├── rubric.py # grading prompt + dimension definitions
├── grader.py # judge-model call + score parsing
├── compressor_driver.py # thin wrapper over ContextCompressor
└── results/ # gitignored; timestamped output per run
└── .gitkeep
```
`scripts/` is the right home: offline tooling, no CI involvement,
precedent already set by `sample_and_compress.py`,
`contributor_audit.py`, `discord-voice-doctor.py`.
`environments/` is for Atropos RL training environments — wrong shape.
`tests/` is hermetic and credential-free — incompatible with a
probe-based eval that needs a judge model.
## Fixture format
A fixture is a single compressed-enough conversation captured from a
real session. Stored as JSON (pretty-printed, reviewable in PRs):
```json
{
"name": "401-debug",
"description": "178-turn session debugging a 401 on /api/auth/login",
"model": "anthropic/claude-sonnet-4.6",
"context_length": 200000,
"messages": [
{"role": "system", "content": "..."},
{"role": "user", "content": "..."},
{"role": "assistant", "content": "...", "tool_calls": [...]},
{"role": "tool", "tool_call_id": "...", "content": "..."}
],
"notes": "Captured 2026-04-24 from session 20260424_*.jsonl; \
PII scrubbed; secrets redacted via redact_sensitive_text."
}
```
### Sourcing fixtures
Fixtures are scrubbed snapshots of real sessions from the
maintainer's `~/.hermes/sessions/*.jsonl` store, generated
reproducibly by `scrub_fixtures.py` in this directory. Re-run the
scrubber with `python3 scripts/compression_eval/scrub_fixtures.py`
to regenerate them after a scrubber change.
Three shipped fixtures cover three different session shapes:
| Fixture | Source shape | Messages | Tokens (rough) | Tests |
|---|---|---|---|---|
| `feature-impl-context-priority` | investigate → patch → test → PR → merge | 75 | ~17k | continuation, artifact trail (2 files modified, 1 PR) |
| `debug-session-feishu-id-model` | PR triage + upstream docs + decision | 59 | ~13k | recall (PR #, error shape), decision (outcome + reason) |
| `config-build-competitive-scouts` | iterative config: 11 cron jobs across 7 weekdays | 61 | ~23k | artifact trail (which jobs, which days), iterative-merge |
The `~17k-23k` token range is below the default 50%-of-200k
compression threshold, so the eval will always **force** a
`compress()` call rather than wait for the natural trigger. That is
the intended shape — we want a controlled single-shot compression so
score deltas are attributable to the prompt change, not to whether
the threshold happened to fire at the same boundary twice.
### Scrubber pipeline
`scrub_fixtures.py` applies, per message:
1. `agent.redact.redact_sensitive_text` — API keys, tokens,
connection strings
2. Username paths: `/home/teknium``/home/user`
3. Personal handles: all case variants of the maintainer name → `user`
4. Email addresses → `contributor@example.com`; git
`Author: Name <addr>` header lines normalised
5. `<REASONING_SCRATCHPAD>...</REASONING_SCRATCHPAD>` and
`<think>...</think>` stripped from assistant content
6. Messaging-platform user mentions (`<@123456>`, `<@***>`) →
`<@user>`
7. First user message paraphrased to remove personal voice;
subsequent user turns kept verbatim after the redactions above
8. System prompt replaced with a generic public-safe placeholder so
we don't check in the maintainer's tuned soul/skills/memory system
block
9. Orphan empty-assistant messages (artifact of scratchpad-only
turns) and trailing tool messages with no matching assistant are
dropped
10. Tool outputs longer than 2000 chars are truncated with a size
annotation; the compressor sees that the tool was called and
returned something but not the full 16KB skill_view or 5KB
web_extract body (no signal loss for compression probes)
Before every fixture PR: grep the fixture for PII patterns. An
audit is embedded at the bottom of the scrubber as comments.
**Fixtures must stay small.** Target <150 KB per fixture, <500 KB
total for the directory. Current total: ~230 KB across three
fixtures. Larger sessions are truncated with a
`truncated_to: <index>` field in the fixture header so the cut is
reviewable.
## Probe format
One probe file per fixture, so reviewers can see the question bank
evolve alongside the fixture:
```json
{
"fixture": "401-debug",
"probes": [
{
"id": "recall-error-code",
"type": "recall",
"question": "What was the original error code and endpoint?",
"expected_facts": ["401", "/api/auth/login"]
},
{
"id": "artifact-files-modified",
"type": "artifact",
"question": "Which files have been modified in this session?",
"expected_facts": ["session_store.py", "redis_client.py"]
},
{
"id": "continuation-next-step",
"type": "continuation",
"question": "What should we do next?",
"expected_facts": ["re-run the integration tests", "restart the worker"]
},
{
"id": "decision-redis-approach",
"type": "decision",
"question": "What did we decide about the Redis issue?",
"expected_facts": ["switch to redis-py 5.x", "pooled connection"]
}
]
}
```
The four probe types come directly from Factory's methodology:
**recall, artifact, continuation, decision**. `expected_facts` gives
the grader concrete anchors instead of relying purely on LLM taste.
Authoring a probe bank is a one-time cost per fixture. 8-12 probes per
fixture is the target — enough to cover all four types, few enough to
grade in under a minute at reasonable cost.
## Grading
Each probe gets scored 0-5 on **six dimensions** (Factory's six):
| Dimension | What it measures |
|-----------------------|-----------------------------------------------------|
| accuracy | File paths, function names, error codes are correct |
| context_awareness | Reflects current state, not a mid-session snapshot |
| artifact_trail | Knows which files were read / modified / created |
| completeness | Addresses all parts of the probe |
| continuity | Agent can continue without re-fetching |
| instruction_following | Probe answered in the requested form |
Grading is done by a single judge-model call per probe with a
deterministic rubric prompt (see `rubric.py`). The rubric includes the
`expected_facts` list so the judge has a concrete anchor. Default
judge model: whatever the user has configured as their main model at
run time (same resolution path as `auxiliary_client.call_llm`). A
`--judge-model` flag allows overriding for consistency across runs.
Non-determinism caveat: two runs of the same fixture will produce
different scores. A single run means nothing. Report medians over
N=3 runs by default, and require an improvement of >=0.3 on any
dimension before claiming a prompt change is a win.
## Run flow
```
python scripts/compression_eval/run_eval.py [OPTIONS]
```
Options (fire-style, mirroring `sample_and_compress.py`):
| Flag | Default | Purpose |
|------------------------|------------|-------------------------------------------|
| `--fixtures` | all | Comma-separated fixture names |
| `--runs` | 3 | Runs per fixture (for median) |
| `--judge-model` | auto | Override judge model |
| `--compressor-model` | auto | Override model used *inside* the compressor |
| `--label` | timestamp | Subdirectory under `results/` |
| `--focus-topic` | none | Pass-through to `compress(focus_topic=)` |
| `--compare-to` | none | Path to a previous run for diff output |
Steps per fixture per run:
1. Load fixture JSON and probe bank.
2. Construct a `ContextCompressor` against the fixture's model.
3. Call `compressor.compress(messages)` — capture the compressed
message list.
4. For each probe: ask the judge model to role-play as the continuing
agent with only the compressed state, then grade the answer on the
six dimensions using `rubric.py`.
5. Write a per-run JSON to `results/<label>/<fixture>-run-N.json`.
6. After all runs, emit a markdown summary to
`results/<label>/report.md`.
## Report format
Pasted verbatim into PR descriptions that touch the compressor:
```
## Compression eval — label 2026-04-25_13-40-02
Main model: anthropic/claude-sonnet-4.6 Judge: same
3 runs per fixture, medians reported.
| Fixture | Accuracy | Context | Artifact | Complete | Continuity | Instruction | Overall |
|----------------|----------|---------|----------|----------|------------|-------------|---------|
| 401-debug | 4.1 | 4.0 | 2.5 | 4.3 | 3.8 | 5.0 | 3.95 |
| pr-review | 3.9 | 3.8 | 3.1 | 4.2 | 3.9 | 5.0 | 3.98 |
| feature-impl | 4.0 | 3.9 | 2.9 | 4.1 | 4.0 | 5.0 | 3.98 |
Per-probe misses (score < 3.0):
- 401-debug / artifact-files-modified: 1.7 — summary dropped redis_client.py
- pr-review / decision-auth-rewrite: 2.3 — outcome captured, reasoning dropped
```
## Cost expectations
Dominated by the judge calls. For 3 fixtures × 10 probes × 3 runs =
90 judge calls per eval run. On Claude Sonnet 4.6 that is roughly
$0.50-$1.50 per full eval depending on probe length. The compressor
itself makes 1 call per fixture × 3 runs = 9 additional calls.
**This is not a check to run after every commit.** It is a
before-merge check for PRs that touch:
- `agent/context_compressor.py` — any change to `_template_sections`,
`_generate_summary`, or `compress()`.
- `agent/auxiliary_client.py` — when changing how compression tasks
are routed.
- `agent/prompt_builder.py` — when the compression-note phrasing
changes.
## Open questions (to resolve before implementing)
1. **Fixture scrubbing: manual or scripted?** A scripted scrub that
also replaces project names / hostnames would lower the cost of
contributing a new fixture. Risk: over-aggressive replacement
destroys the signal the probe depends on. Propose: start manual,
add scripted helpers once we have 3 fixtures and know the common
PII shapes.
2. **Judge model selection.** Factory uses GPT-5.2. We can't pin one
— user's main model changes. Options: (a) grade with main model
(cheap, inconsistent across users), (b) require a specific judge
model (e.g. `claude-sonnet-4.6`), inconsistent for users without
access. Propose (a) with a `--judge-model` override, and make the
model name prominent in the report so comparisons across machines
are legible.
3. **Noise floor.** Before landing prompt changes, run the current
prompt N=10 times to measure per-dimension stddev. That tells us
the minimum delta to call a change significant. Suspect 0.2-0.3 on
a 0-5 scale. Decision deferred until after the first fixture is
landed.
4. **Iterative-merge coverage.** The real Factory-vs-Anthropic
difference is incremental merge vs. regenerate. A fixture that
only compresses once doesn't exercise our iterative path. Add a
fourth fixture that forces two compressions (manually chained),
with probes that test whether information from the first
compression survives the second. Deferred to a follow-up PR.
## Implementation order
This PR: design doc + scaffolding + **three checked-in fixtures** +
scrubber script. `run_eval.py` is still a placeholder that prints a
pointer to DESIGN.md.
Follow-ups, each a separate PR:
1. Probe banks for the three fixtures (~8-12 probes each), plus
`rubric.py` + `grader.py` + `compressor_driver.py`. Enough to
produce a full report.
2. Wire results output, `--compare-to` diff mode, and the report
markdown template.
3. Iterative-merge fixture (two chained compressions) + follow-ups
from the open questions.
Each follow-up is independently useful.