docs: make the repository legible to open-source readers, and license it

CONTRIBUTING.md

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+# Contributing to ContextEngine
+
+Thanks for taking the time to look at this project.
+
+Before you write code, please read this page. ContextEngine holds a stricter
+evidence bar than most repositories its size, and the difference is not style —
+it is the point of the project. A contribution that adds a useful feature but
+weakens an invariant will be declined.
+
+## The one rule that explains all the others
+
+**Security is a veto, not a score.**
+
+Three invariants must hold, and no feature benefit offsets a failure in any of
+them:
+
+- Unauthorized Evidence leaked = **0**
+- Wrong-Organization effect = **0**
+- Missing tenant context = **fail closed, always**
+
+A second rule follows from the first: **a capability is not "done" because it
+runs — it is done when executable evidence proves its exact boundary.**
+Anything unproven stays labeled `NOT_ACTIVE`, including in the service's own
+`/health` response. Please do not "helpfully" remove a `NOT_ACTIVE` marker; it
+is load-bearing. See [STATUS.md](./STATUS.md).
+
+## Before you start
+
+1. **Check the issue tracker.** Issues and PRDs live in
+   [GitHub Issues](https://github.com/stone16/context-engine/issues). Read the
+   full body, labels, and comments before acting on an existing issue.
+2. **Open an issue before a large PR.** External pull requests are not a triage
+   surface for feature requests — an unsolicited large PR is likely to be
+   declined on scope alone, however good the code is.
+3. **Read the domain glossary.** [CONTEXT.md](./CONTEXT.md) is the repository's
+   authority on terms like `CandidateRef`, `AuthorizedProjection`,
+   `SourceAclEvidence`, and `TrustedDeliveryContext`. Using these words loosely
+   in code or review is a real source of bugs here.
+
+### Triage labels
+
+| Label | Meaning |
+|---|---|
+| `needs-triage` | Maintainer evaluation is required |
+| `needs-info` | Waiting for reporter information |
+| `ready-for-agent` | Fully specified and AFK-agent ready |
+| `ready-for-human` | Human implementation or judgment is required |
+| `wontfix` | The work will not be actioned |
+
+## Development setup
+
+See [Quick start](./README.md#quick-start) in the README for prerequisites
+(Python 3.13, uv, Node 22.12.0, Docker).
+
+```bash
+make install
+make db-up
+```
+
+## The verification contract
+
+**Never claim a change works without running the commands and reading the real
+output.** Fabricated or assumed verification output is the one contribution
+behavior that will get a PR closed without further review.
+
+Run the full gate — the same one CI runs — before opening a PR:
+
+```bash
+make check
+```
+
+`make check` requires `make db-up` first, and covers: build, Ruff, strict mypy,
+TypeScript typecheck, OpenAPI freeze check, SDK generate/build/test/pack,
+ActionPlane and BotDelivery build and tests, Python unit tests, the security
+catalog, the process smoke suite, the real-PostgreSQL integration harness, and
+the M0 security gate.
+
+For faster inner loops:
+
+```bash
+make lint          # Ruff
+make typecheck     # strict mypy + TS
+make test          # Python unit tests
+make integration   # real-PostgreSQL integration/security harness
+make security-gate # M0 security veto gate
+```
+
+When you are done, stop the harness:
+
+```bash
+make db-down
+```
+
+## Writing tests
+
+Tests are not a coverage exercise here — they are the evidence the project
+ships on. Two expectations go beyond the usual:
+
+- **A test must encode the business invariant it protects,** not merely the
+  current behavior. If a test still passes after the meaningful rule changes,
+  it is a shallow test.
+- **Runtime tests use the highest public seam available** — HTTP or the
+  generated SDK — and must prove the chain
+  `CandidateRef → AuthorizationKernel → AuthorizedProjection`. A test that lets
+  a raw candidate reach a content-bearing consumer is testing the wrong thing.
+
+Negative cases matter as much as positive ones: cross-Organization, denied
+same-Organization, nonexistent candidates, tampering, replay, expiry, and
+concurrent losers should all be provably zero-effect.
+
+## Architectural boundaries
+
+These are not preferences. Changes that cross them will be asked for an ADR
+first, or declined.
+
+- **The Runtime path is sealed, not merely wired.** No feature flag, alternate
+  composition, no-op dependency, or direct retriever-to-assembler path may
+  bypass the `AuthorizationKernel`, PackageBudget, provenance, or audit gates.
+- **Authorization precedes anything content-bearing.** Indexes return
+  `CandidateRef` only. Hydration, reranking, relevance models, and assembly
+  accept `AuthorizedProjection` only. Every parent/neighbor expansion is
+  re-authorized.
+- **`Weak` ACL evidence is never a fallback.** It is permitted only where a
+  source genuinely lacks finer-grained ACL semantics. A failed `Live` or
+  `Mirrored` check fails closed.
+- **External effects go through `ActionPlane.prepare` then `perform`,** each
+  with its own org-scoped, audience- and payload-bound, one-shot ticket. Never
+  reuse a create ticket for an edit or send.
+- **Index and cache filters never make authorization decisions.**
+- **No secrets, `.env` values, or credentials in commits** — reference a single
+  live source. Do not hardcode volatile values (URLs, ports, versions) in prose;
+  point to their source of truth.
+
+### Zero code copying
+
+The design draws on architectural study of **Dify**, **RAGFlow**, **MaxKB**, and
+**Onyx**, limited to observable behavior, interface shape, test oracles, and
+product workflows. **Do not copy code from them, in any amount.** Public
+reference claims must trace to the
+[evidence baseline](./docs/research/2026-07-19-four-public-repositories-evidence.md).
+Research from outside this repository may inform your reasoning, but must never
+be cited or linked as public provenance.
+
+## Architecture Decision Records
+
+Any non-obvious decision is recorded as an ADR under
+[`docs/decisions/`](./docs/decisions/README.md) — there are 60 of them, and they
+are the authority on boundaries, dependency direction, forbidden shortcuts, and
+revisit triggers.
+
+Write a new ADR when your change alters a boundary, introduces a dependency
+direction, or closes off an option that a future contributor might reasonably
+want. Follow the numbering and shape of the most recent accepted ADRs.
+
+## Pull requests
+
+**Commits.** One concern per commit. Use the prefixes already in the history:
+`feat:`, `fix:`, `docs:`, `chore:`, `refactor:`, `style:`, or a domain prefix
+such as `supply:`, `runtime:`, `delivery:`, `bot:`.
+
+**Before you open the PR, confirm:**
+
+- [ ] The change does what the issue asked, and edge cases are considered.
+- [ ] `make check` passes, and you have the real output — not an assumption.
+- [ ] Runtime tests prove `CandidateRef → AuthorizationKernel →
+      AuthorizedProjection`; no raw candidate reaches a content-bearing consumer.
+- [ ] No secrets or volatile values baked into code or docs.
+- [ ] Any non-obvious decision is recorded as an ADR.
+- [ ] Capability claims match reality — anything unproven is still `NOT_ACTIVE`,
+      and [STATUS.md](./STATUS.md) is updated if a boundary moved.
+
+**In the PR description**, state plainly what you verified and what you did not.
+If you skipped something, say so. Surfacing uncertainty is always preferred to
+hiding it.
+
+## Scope discipline
+
+Touch only what the task requires. Please do not "improve" adjacent code,
+comments, or formatting in the same PR — it makes the security-relevant diff
+harder to review, which is a real cost in this repository. Match existing
+conventions even where you would have chosen differently; if you think a
+convention is harmful, raise it as its own issue rather than forking it
+silently.
+
+## License
+
+By contributing, you agree that your contributions are licensed under the
+[Apache License 2.0](./LICENSE).

LICENSE

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