docs(plan): brief for delete-and-rebuild (config subtraction axis)

Operator relayed the "delete your CLAUDE.md every six months" idea from a
third-party summary of a Boris Cherny talk. Assessed rather than adopted: the
provenance is secondhand and deliberately kept non-load-bearing (this repo has
one scar from treating a plausible quote as fact), while the feature is argued
from the repo's own logic.

The gap is real and verified, not assumed: feature-gap has no inverse, and grep
over scanners/ confirms nothing measures instruction AGE — 'stale' appears only
for knowledge-register entries and plugin-cache versions. drift's saveBaseline/
diffEnvelopes plus backup.mjs/rollback-engine.mjs are already the undo
machinery that makes deletion a measurement rather than a gamble.

CLI ground truth checked against claude --help: --bare (sets
CLAUDE_CODE_SIMPLE=1), --system-prompt, --setting-sources, --add-dir. So the
env var the video calls undocumented is a documented flag here, which is what
would make an ablation harness buildable.

Brief only — no code, no chunk breakdown, no version committed. Three candidate
shapes with a likely landing (deterministic CA-VIN vintage scanner first),
hard constraints, open questions, and testable verification criteria.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JNrtHo9hKSLKNyMS6b4Zuy

docs/delete-and-rebuild-brief.md

@@ -0,0 +1,158 @@
+# 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).