docs: add a five-minute first-contribution path

CONTRIBUTING.md

@@ -2,6 +2,9 @@
 
 Thank you for helping build open infrastructure for economically disciplined AI agents.
 
+New here? [First contribution in 5 minutes](docs/project/first-contribution.md) shows where a small,
+low-risk change can start and the shortest loop that validates it. The standards below still apply.
+
 ## Principles
 
 Contributions must preserve these properties:

docs/index.md

@@ -42,6 +42,7 @@ MARGINAL documentation is organized by user intent instead of keeping every guid
 
 ## Project
 
+- [First contribution in 5 minutes](project/first-contribution.md)
 - [Governance](project/governance.md)
 - [Community feedback](project/community-feedback.md)
 - [Roadmap](../ROADMAP.md)

docs/project/first-contribution.md

@@ -0,0 +1,98 @@
+# First contribution in 5 minutes
+
+`CONTRIBUTING.md` describes the standards a change has to meet. This page is
+the other half: where a small, low-risk change can start, and the shortest loop
+that proves it works.
+
+Nothing here relaxes those standards. The privacy, benchmark, and compatibility
+requirements in [`CONTRIBUTING.md`](../../CONTRIBUTING.md) apply to a one-line
+documentation fix exactly as they apply to a new adapter.
+
+## Set up
+
+```bash
+git clone https://github.com/SignalLayerLabs/Marginal.git
+cd Marginal
+python -m venv .venv
+source .venv/bin/activate        # Windows: .venv\Scripts\activate
+python -m pip install -e ".[dev]"
+```
+
+## Run one focused test
+
+While iterating, run only the tests you are touching:
+
+```bash
+pytest tests/test_budget.py -q
+```
+
+A single file returns in about a second, which is what makes an edit-run loop
+worth having. Narrow further with `-k`:
+
+```bash
+pytest tests/test_budget.py -q -k reservation
+```
+
+## Run the full checks before opening a pull request
+
+```bash
+ruff format --check src tests examples
+ruff check src tests examples
+mypy src/marginal
+pytest -q
+python -m build
+python -m twine check dist/*
+```
+
+Run these before pushing, not after review. They are the same checks a reviewer
+would otherwise run for you.
+
+## Where a first change can safely start
+
+### Documentation
+
+The lowest-risk area, and the easiest place to be genuinely useful: a
+definition that is stated in two places and has drifted, a step that no longer
+matches the code, a missing link. Documentation must not broaden a capability
+claim: the Observe / Tool Enforcement / Full Compute Enforcement labels in the
+[integration overview](../integrations/overview.md#integration-labels) are the
+ones to be most careful with.
+
+### Synthetic fixtures
+
+New test fixtures are welcome, with one hard rule.
+
+**Examples and fixtures must use synthetic identifiers.** Never commit real
+customer, repository, model, incident, or employee names as telemetry fixtures.
+This is not a style preference -- fixtures end up in exports, and a real name in
+a fixture is a privacy incident that outlives the pull request. Use obviously
+invented values such as `repo-alpha`, `session-0001`, `user-a`.
+
+### Examples
+
+The scripts in `examples/` are executable and must stay runnable:
+
+```bash
+python examples/shadow_mode.py
+python examples/universal_runtime.py
+```
+
+If you change a public API these exercise, run them. The same synthetic
+identifier rule applies.
+
+### Focused tests
+
+Existing behavior that has no test is a good first contribution: it needs no
+design decision, and it makes the next refactor safer.
+
+Note the asymmetry in `CONTRIBUTING.md` -- *new behavior* requires a failing
+test written **before** the implementation. Adding coverage for behavior that
+already exists is the easier case, and the one to start with.
+
+## What to expect in review
+
+Pull requests should stay focused, and should explain the problem, interface,
+behavior, validation, compatibility, privacy, and scientific limitations that
+apply. Not every heading is relevant to every change -- a typo fix has no
+scientific limitations -- but a reviewer should not have to ask which ones you
+considered.