config-audit/docs/delete-and-rebuild-brief.md

Brief — Delete-and-Rebuild (config subtraction)

Status: BRIEF, not a plan. No code, no chunk breakdown, no version number committed. Written 2026-07-29 so a session starting Thursday evening has a durable starting point. STATE.md is gitignored in this repo, so this file — not STATE — is the record.

---

1. Trigger and its provenance

The operator relayed a third-party YouTube summary (Hyper Automation Labs) of a talk Boris Cherny reportedly gave at Y Combinator Startup School, one day after Opus 5 shipped. Claims attributed to him in that summary:

• Anthropic deleted ~80 % of Claude Code's own system prompt when Opus 5 landed.
• Advice to users: every six months, delete your CLAUDE.md, your skills, your hooks — see what the model does.
• Rebuild method: delete everything, use it, add one line back only when the model stumbles on the same thing repeatedly.
• The model measured slightly more intelligent with the built-in prompts stripped.

None of this is verified. It is a secondhand transcript of a talk, from a channel selling a lead-magnet PDF. It is recorded here as the trigger, and it is deliberately not load-bearing for anything below. This repo already has one scar from treating a plausible quote as fact («Fable low ≈ Opus high», fabricated, rejected 2026-07-14).

If the attribution ever needs to matter — e.g. if this becomes a BP-* entry in the best-practices register — it needs a primary source (the YC talk itself, or an Anthropic doc), and until then the register's source field must read "third-party video summary, unverified". Verification is a Thursday task, not a prerequisite: the feature justifies itself from this repo's own logic (§3).

2. Verified ground truth (checked against the local CLI, 2026-07-29)

These are facts, and they are what make an empirical variant buildable:

Fact	How verified
claude --bare exists — "Minimal mode: skip hooks, LSP, plugin sync, attribution, auto-memory, background prefetches, keychain reads, and CLAUDE.md auto-discovery. Sets CLAUDE_CODE_SIMPLE=1."	claude --help
claude --system-prompt <prompt> — replaces the session system prompt	claude --help
--append-system-prompt, --add-dir, --setting-sources <user,project,local>, --plugin-dir, --settings, --agents — all present and all usable to compose an isolated config for a controlled run	claude --help

So the CLAUDE_CODE_SIMPLE=1 env var the video calls "undocumented" is, in this CLI version, a documented flag (--bare). That matters: an A/B ablation harness would not need an undocumented hook.

3. Why this fits this repo (the argument that does not depend on §1)

The plugin has three pillars — Health, Opportunities, Action. Every existing command answers a question on the addition axis:

• feature-gap — what could you add?
• optimize — what would fit a better mechanism?
• posture / tokens / manifest — how good/expensive is what you have?
• fix / implement — apply changes.

Nothing answers the subtraction question: what is no longer earning its rent? feature-gap has no inverse. That is a real hole, independent of who said what on a stage.

Two further reasons this belongs here specifically:

1. Nothing in the repo measures instruction age. Verified by grep over scanners/: stale appears only for knowledge-register entry age (lib/knowledge-refresh.mjs) and for stale plugin-cache versions (scan-orchestrator.mjs, M-BUG-11). No scanner touches git blame, mtime, or the vintage of a CLAUDE.md block. An instruction written for Sonnet 3.5 and an instruction written last week are indistinguishable to every current scanner.
2. Deleting bravely is only sane if you can undo it. That is already pillar three: lib/backup.mjs, rollback-engine.mjs, auto-backup-config.mjs (PreToolUse), and drift's saveBaseline / loadBaseline / diffEnvelopes. The safety net exists; the feature that would use it does not. This is arguably the strongest framing: config-audit is already the infrastructure that makes "delete it and see" a measurement rather than a gamble.

4. Reusable machinery (do not rebuild these)

Need	Already exists
Snapshot config before deleting	scanners/lib/baseline.mjs (saveBaseline), used by drift
Diff before/after	diffEnvelopes in the same module
Backup + restore individual files w/ sha256 manifest	scanners/lib/backup.mjs, scanners/rollback-engine.mjs
Cost of each source, always-loaded subtotal	scanners/manifest.mjs, token-hotspots.mjs
Human-approved-writes command pattern	knowledge-refresh, campaign (both non-byte-stable by design)

5. Candidate shapes (sketches — pick on Thursday, do not pre-commit)

A. Deterministic vintage scanner (CA-VIN-*). Per instruction block in CLAUDE.md / rules / skills / hooks: age from git history, plus a compensatory-phrasing signal (blocks that exist to correct model behaviour — "ALWAYS", "never forget", "read the whole file first", "don't guess"). Output: ranked deletion candidates with age + token cost + why it looks compensatory. Cheapest, most testable, fits the existing scanner architecture, and composes with tokens/manifest for the payoff figure. Caveat: ~/.claude is not git-tracked, so age there falls back to mtime, which is weaker evidence. Project-level CLAUDE.md/rules get real git ages.

B. Protocol command (/config-audit rebuild). The delete → live with it → earned re-add ledger loop, spanning sessions: archive current config, record what was archived, and maintain a ledger where a line only returns when the operator records that the model actually stumbled on it. Highest fidelity to the source idea; needs cross-session state (the sessions/ machinery already exists) and is inherently not byte-stable.

C. Measured ablation harness. Use --bare + --system-prompt/--add-dir to run the same prompt with and without a block and compare. Closest to a real verifier, most expensive in tokens, weakest determinism. Probably a later --experimental sub-mode of A or B rather than its own command.

Likely landing: A first (deterministic, testable, immediately useful), with B as the workflow that consumes A's output. C stays a documented idea until A+B exist.

6. Hard constraints (carry these into any implementation)

• ~/.claude is NOT git-tracked. A literal rm there is unrecoverable. Archive by mv into _archive/, never delete. This is already an inviolable rule in STATE.md.
• settings.json is pathguard-protected — no Edit/Write. Use jq + temp file + atomic mv, with operator OK (settings-json-pathguard-write).
• New scanner ⇒ the 7-step byte-stability checklist (adding-scanner-byte-stability): scanner + orchestrator + scoring area-map + strip-added-scanner + humanizer count + SC-5 + humanizer wiring (SCANNER_TO_CATEGORY entry and TRANSLATIONS.static per RAW title — M-16/M-17). Frozen tests/snapshots/v5.0.0/ must stay untouched.
• TDD is inviolable — red tests before implementation, including for .md contracts.
• feat: commits require non-trivial diffs in both README.md and CLAUDE.md (docs-gate-feat-requires-readme-claudemd).

7. Open questions for Thursday

1. Scope of the deletion candidate set: user-level ~/.claude only, project only, or both? (Age evidence is much stronger for project-level, per §5A.)
2. Is "compensatory phrasing" detectable with acceptable precision, or does it need the agent layer (like optimize's precision-gated optimization-lens-agent)?
3. Does this ship as its own command, or as a --subtract mode of optimize? Both are defensible; command count is already 21.
4. Ordering against the existing queue: pipeline step 4 rollback, then the M-11→M-20 batch release, then the v5.13 plan. See STATE.md.

8. Verifisering (testable criteria)

Before building anything:

• grep -rniE 'blame|mtime|birthtime' scanners/ returns no instruction-age handling → confirms §3.1 still true at build time.
• node scanners/drift-cli.mjs <path> --save --name pre-subtraction succeeds and lib/baseline.mjs round-trips → confirms §4 reuse is real, not assumed.
• If any claim from §1 is to be written into the register: a primary source exists (URL to the talk or an Anthropic doc). Otherwise the entry is not written.

If shape A is built:

• Red tests exist and fail before implementation.
• node --test 'tests/**/*.test.mjs' green, count strictly greater than 1365.
• git diff --stat tests/snapshots/v5.0.0/ is empty (frozen baselines untouched).
• node scanners/self-audit.mjs --check-readme passes (badge counts updated: scanners 16 → 17).
• Every new finding renders with a non-Other userImpactCategory and a non-_default action language → humanizer wiring correct (M-16/M-17).
• Dogfood on this machine produces at least one candidate the operator agrees is genuinely dead weight, and zero candidates the operator judges load-bearing (precision over recall — a false "delete this" is far more costly than a miss).