Add Copilot custom instructions and bounded test-first intake prompt file

.github/copilot-instructions.md

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+# Copilot Instructions — constraint-workshop
+
+## Repo identity
+
+This repository holds small, deterministic control primitives.
+Every primitive is a single file + a test file. No frameworks. No runtime dependencies. No hidden state.
+
+## Invariant files — DO NOT MODIFY
+
+The following files are **frozen**. Never edit, refactor, rename, or delete them:
+
+- `authority_gate.py`
+- `stop_machine.py`
+- `invariant_litmus.py`
+- `commit_gate/` (entire directory)
+
+If any suggestion would touch these paths, stop and say so instead of making the change.
+
+## Bounded intake rule
+
+**No implementation code may be generated until all of the following are true:**
+
+1. A schema (data shape + field constraints) for the new primitive exists in a `.py` or `.md` file.
+2. Golden tests exist that assert specific, pinned expected values (not just "it doesn't crash").
+3. All golden tests are collected by `pytest` and initially fail with `NotImplementedError` or an import error — proving the tests are real and the implementation does not yet exist.
+
+Refusing to proceed past this gate is correct behaviour, not a bug.
+
+## Test-first order
+
+When asked to build a new primitive, always do work in this order:
+
+1. **Schema** — define data types, enumerations, and field constraints only. No logic.
+2. **Golden tests** — write `pytest` tests that pin exact expected outputs for known inputs. Tests must fail until step 3.
+3. **Implementation** — only after the user confirms the tests fail as expected.
+
+Do not collapse these steps. Do not combine schema + implementation in one pass.
+
+## Style rules
+
+- Stdlib only. Do not add third-party imports unless the user explicitly approves.
+- No global mutable state.
+- No `random`, `uuid`, `time.time()`, `datetime.now()`, or `os.getpid()` in any primitive.
+- All public functions must be pure (same input → same output, always).
+- Test files are named `test_<module>.py` and live in the repo root (or `<subpackage>/tests/`).
+
+## CI contract
+
+CI runs `pytest -q` across Python 3.10, 3.11, 3.12.
+A PR is not ready to merge until `pytest -q` passes with zero failures.
+
+## Out of scope
+
+Do not generate: orchestration layers, policy engines, selection logic, ML models, HTTP clients, database connections, or logging frameworks.
+`/prometheus` is the observability-only sub-package (`prometheus/src/prometheus/`). It aggregates diagnostic events and reports health posture. It must not be imported by any gate, primitive, or pipeline code.

.github/prompts/commitboundary_spec_intake.prompt.md

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+# CommitBoundary Spec Intake
+
+Use this prompt file to introduce a new primitive or spec change in a bounded, test-first way.
+Run it from VS Code: **Command Palette → "Chat: Run Prompt"**, then select this file.
+
+---
+
+## Step 0 — Gate check
+
+Before generating anything, confirm:
+
+- [ ] The request does **not** touch `authority_gate.py`, `stop_machine.py`, `invariant_litmus.py`, or `commit_gate/`.
+
+If it does, **stop here** and tell the user which protected file would be affected. Do not proceed.
+
+---
+
+## Step 1 — Schema only
+
+Generate a schema file named `<primitive_name>_schema.py` containing:
+
+- Enumerations or `TypedDict`/`NamedTuple` definitions for every data type the primitive will use.
+- Field-level constraints as inline docstrings (e.g., "must be non-negative", "immutable after construction").
+- A `SCHEMA_VERSION` string constant (start at `"0.1"` for new primitives; increment the minor version when updating an existing schema).
+- **No logic. No methods beyond `__repr__`. No `__init__` that does computation.**
+
+Do **not** generate an implementation file yet.
+
+---
+
+## Step 2 — Golden tests (fail-first)
+
+Generate a test file named `test_<primitive_name>.py` containing:
+
+- At least three test functions that assert **exact, pinned expected values** for known inputs.
+- One test that asserts a `TypeError` or `ValueError` is raised for invalid inputs.
+- One test that asserts the function/class raises `NotImplementedError` when called (proving the stub is not yet implemented).
+- Import the module as if it exists: `from <primitive_name> import ...`
+
+**All tests must fail** until the implementation exists. Confirm this by noting at the bottom of the file:
+
+```python
+# FAIL-FIRST: these tests must fail until the implementation is complete.
+```
+
+Do **not** generate an implementation file yet.
+
+---
+
+## Step 3 — User confirmation gate
+
+At this point, output a summary checklist:
+
+```
+Schema file:      <primitive_name>_schema.py        ✓ generated
+Golden tests:     test_<primitive_name>.py           ✓ generated (expect failures)
+
+Next step: run `pytest test_<primitive_name>.py -v` and confirm all tests fail.
+Reply "tests fail as expected" to unlock Step 4.
+```
+
+**Do not proceed to Step 4 without the user's confirmation.**
+
+---
+
+## Step 4 — Implementation
+
+Only after the user confirms the tests fail:
+
+1. Generate `<primitive_name>.py` with the minimal implementation that makes all golden tests pass.
+2. Do not add features not covered by the golden tests.
+3. Stdlib only — no third-party imports unless the user explicitly approved them in this session.
+4. After generating, output the command to verify:
+
+```
+pytest test_<primitive_name>.py -v
+```
+
+---
+
+## Step 5 — Final checklist
+
+After implementation:
+
+```
+Schema:           <primitive_name>_schema.py        ✓
+Golden tests:     test_<primitive_name>.py           ✓ (all passing)
+Implementation:   <primitive_name>.py               ✓
+CI command:       pytest -q                         (run to confirm nothing regressed)
+Protected files:  authority_gate.py / stop_machine.py / invariant_litmus.py / commit_gate/   ✓ untouched
+```
+
+Do not open a PR until this checklist is complete.