feat(skills): import Spec-Driven Development (SDD) suite

- Add grill: calibrated plan stress-testing before speccing
- Add spec: sole mutator of SPEC.md with format specification
- Add caveman: token-compression dialect for invariants and tasks
- Add review: adversarial pre-implementation refutation of spec
- Add build: single-threaded plan-to-execute loop with external oracles
- Add check: read-only drift detector comparing code vs invariants
- Add backprop: bug-to-spec feedback loop binding regression tests
- Add deepen: complexity reduction and interface shrinking pass
- Format all skills to 5-phase Skill Architect anatomy with System One balance
- Synchronize symlinks across OpenCode, Codex, and Claude Code

skills/check/SKILL.md

@@ -0,0 +1,98 @@
+---
+name: check
+description: >
+  Read-only drift detector comparing SPEC.md against current codebase.
+  Audits invariants (§V), interface shapes (§I), and task completion (§T), reporting violations with file:line citations.
+  Use when asked to "check drift", "audit spec", "spec vs code", or before releasing.
+concerns: [system-one-balance]
+---
+
+# Check — Drift Detector
+
+Pure diagnostic audit. Reports violations and interface drift. Strictly read-only; writes nothing.
+
+Spec drifting silently from code is the primary failure mode of long-lived projects. `check` catches drift before it becomes production defects.
+
+---
+
+## Phase 0: Setup and Protocols
+
+1. **Non-Negotiable Invariants**:
+   - **Zero Writes**: Never edit code or `SPEC.md`. Report findings only.
+   - Every violation must cite `file:line` evidence.
+   - If `SPEC.md` is absent at repo root, report "no spec found" and exit.
+
+---
+
+## Phase 1: Ingest and Check
+
+1. Ingest `SPEC.md` from the project root.
+2. Parse audit scope from arguments:
+   - `§V`: Audit invariants only (default).
+   - `§I`: Audit external interfaces only.
+   - `§T`: Audit task status against reality.
+   - `--all` (or empty): Audit all three sections.
+
+---
+
+## Phase 2: Processing (Core Logic)
+
+### Step 1: Audit Invariants (§V)
+For each `V<n>` invariant:
+1. Translate invariant into a verifiable assertion about code.
+2. Search and inspect corresponding files.
+3. Classify state:
+   - **HOLD**: Invariant actively satisfied with test or code assertion.
+   - **VIOLATE**: Invariant actively violated in implementation.
+   - **UNVERIFIABLE**: Invariant has no corresponding automated test or code guard.
+
+### Step 2: Audit Interfaces (§I)
+For each interface defined in §I:
+1. Locate implementation in routes, CLI, or exported functions.
+2. Classify state:
+   - **MATCH**: Code shape matches §I specification exactly.
+   - **DRIFT**: Implementation exists but signatures, parameters, or return types diverge.
+   - **MISSING**: Interface declared in spec but absent from code.
+   - **EXTRA**: Code exposes public endpoints/flags not documented in §I.
+
+### Step 3: Audit Tasks (§T)
+For each `T<n>` row:
+1. If status is `x`: verify claimed files/tests exist in git. If absent, flag **STALE**.
+2. If status is `~`: note as in-progress.
+3. If status is `.`: note as pending.
+
+---
+
+## Phase 3: The System One Balance Pass
+
+- **Augment, Don't Handcuff**:
+  - Report findings concisely without lecturing or auto-triggering refactors.
+  - Provide actionable remedy hints for each class of drift, leaving decisions to the user.
+
+---
+
+## Phase 4: Output Execution & Verification
+
+Emit the structured Caveman drift report:
+
+```markdown
+## Drift Report
+
+### §V Invariants
+- V2 VIOLATE: src/auth/mw.ts:47 uses `<` instead of `≤`.
+- V5 UNVERIFIABLE: no test covers concurrent refund boundary.
+
+### §I Interfaces
+- I.api DRIFT: POST /v1/charge returns `{result}` instead of `{id}`. routes/charge.py:82.
+- I.cmd MISSING: `limiter bench` absent from CLI definitions.
+
+### §T Tasks
+- T3 STALE: marked `x` but auth middleware file not found in tree.
+
+### Summary
+- X violations, Y drifts, Z missing, W stale.
+- **Remedy Hints**:
+  - VIOLATE / DRIFT: Invoke `spec` with `bug: <V.n>` or fix code at cited lines.
+  - MISSING: Invoke `build §T.n` or `spec amend §T`.
+  - STALE: Invoke `spec amend §T` to reset status.
+```