docs: contributor onboarding path + CODEOWNERS for bus-factor mitigation

.github/CODEOWNERS

@@ -0,0 +1,16 @@
+# Code owners — auto-requested as reviewers on matching paths.
+# Last match wins; see https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-code-owners
+#
+# Review expectation: PR authors wait for at least one CODEOWNERS approval before merge.
+# Do not self-merge without review, even on docs-only changes.
+
+# Default owner for the repository.
+*                       @clean6378-max-it
+
+# Docs and contributor process
+/docs/                  @clean6378-max-it
+/CONTRIBUTING.md        @clean6378-max-it
+/README.md              @clean6378-max-it
+
+# CI and workflow changes
+/.github/               @clean6378-max-it

CONTRIBUTING.md

@@ -2,6 +2,8 @@
 
 Thanks for considering a patch. This repo is a small Flask app plus a hash-routed SPA and a CLI export script. Keep changes focused and tested.
 
+**New contributors:** start with [`docs/onboarding.md`](docs/onboarding.md) for a first-PR walkthrough, suggested reading order, full CI gate commands, and good-first-issue pointers.
+
 ## Development setup
 
 ### Prerequisites

README.md

@@ -143,7 +143,9 @@ claude-code-chat-browser/
 
 ## Development
 
-See **[`CONTRIBUTING.md`](CONTRIBUTING.md)** for full setup, conventions, and where to change each layer.
+See **[`CONTRIBUTING.md`](CONTRIBUTING.md)** for full setup, conventions, and where to change each layer. New contributors should follow **[`docs/onboarding.md`](docs/onboarding.md)** for a first-PR walkthrough and reading order.
+
+**Maintainer coverage:** commit activity is currently concentrated on a small set of identities (bus-factor risk). Mitigations: [`.github/CODEOWNERS`](.github/CODEOWNERS) for review routing and [`docs/onboarding.md`](docs/onboarding.md) so additional contributors can ramp quickly.
 
 Quick start:
 

docs/architecture.md

@@ -151,6 +151,7 @@ No bundler step — modern browsers load modules directly. Frontend unit tests u
 
 ## Related documentation
 
+- [Contributor onboarding](onboarding.md)
 - [API reference](api-reference.md)
 - [Contributing](../CONTRIBUTING.md)
 - [README](../README.md)

docs/onboarding.md

@@ -0,0 +1,126 @@
+# Contributor onboarding
+
+Welcome. This doc is the **fast path** for your first PR. It links the existing guides rather than repeating them — read it once, then bookmark the references below.
+
+## Before you start
+
+| Doc | What it covers |
+|-----|----------------|
+| [CONTRIBUTING.md](../CONTRIBUTING.md) | Dev setup, code style, PR checklist, where to change each layer |
+| [docs/architecture.md](architecture.md) | Data flow, export state machine, dispatch table, frontend layout |
+| [docs/api-reference.md](api-reference.md) | HTTP routes, error codes, field stability |
+
+## Suggested reading order
+
+Work through these in order before touching unfamiliar code:
+
+1. **[docs/architecture.md](architecture.md)** — component diagram, layers, and how JSONL becomes API + UI.
+2. **[utils/jsonl_parser.py](../utils/jsonl_parser.py)** — session parsing entry point; tool results flow through `tool_dispatch`.
+3. **[utils/tool_dispatch.py](../utils/tool_dispatch.py)** — priority-based `_TOOL_RESULT_DISPATCH` table; read the module docstring and [dispatch table notes](architecture.md#dispatch-table).
+4. **Frontend SPA** — [`static/js/app.js`](../static/js/app.js) (routing), [`static/js/sessions.js`](../static/js/sessions.js) (message panel), [`static/js/render/registry.js`](../static/js/render/registry.js) (tool renderers).
+
+For API or export changes, also skim [`api/error_codes.py`](../api/error_codes.py) and [`utils/md_exporter.py`](../utils/md_exporter.py).
+
+## First PR walkthrough
+
+### 1. Fork and clone
+
+```powershell
+# GitHub UI: fork cppalliance/claude-code-chat-browser to your account, then:
+git clone https://github.com/<your-user>/claude-code-chat-browser.git
+cd claude-code-chat-browser
+git remote add upstream https://github.com/cppalliance/claude-code-chat-browser.git
+```
+
+On macOS/Linux, use the same `git clone` / `git remote add` commands in your shell.
+
+### 2. Create a branch
+
+Branch names follow `feat/<topic>`, `fix/<topic>`, `docs/<topic>`, etc. (see [CONTRIBUTING.md](../CONTRIBUTING.md#branching-and-pull-requests)).
+
+```bash
+git fetch upstream
+git checkout -b docs/my-first-change upstream/master
+```
+
+### 3. Development setup
+
+Follow **[CONTRIBUTING.md — Development setup](../CONTRIBUTING.md#development-setup)** for your OS (Python 3.12 venv, `pip install -r requirements-dev.txt`, optional Node 20+ for JS).
+
+Smoke-test the dev server:
+
+```bash
+python app.py --port 5000
+# Open http://127.0.0.1:5000
+```
+
+### 4. Make a focused change
+
+- One logical change per PR when possible.
+- Match existing conventions (ruff, import order, `error_response()` for API errors) — see [Code style](../CONTRIBUTING.md#code-style-and-conventions).
+- Add or update tests for behavior changes — see [Tests required](../CONTRIBUTING.md#tests-required-for-common-changes).
+
+### 5. Run the full local gate
+
+CI runs these on Ubuntu, Windows, and macOS. Run them locally before opening a PR:
+
+```bash
+# Lint + format (required)
+ruff check .
+ruff format --check .
+
+# Type check (Ubuntu CI job; run locally before Python-heavy changes)
+mypy -p api -p utils -p models -p scripts
+
+# Security audit (production deps)
+pip-audit -r requirements.txt
+
+# Python tests (full suite)
+pytest -q
+
+# Integration subset (also run in CI)
+pytest tests/test_api_integration.py -v
+
+# Frontend — only if you changed static/js/
+npm ci
+npm test
+```
+
+Fix formatting with `ruff format .` when `ruff format --check` fails.
+
+### 6. Push and open a PR
+
+```bash
+git push -u origin docs/my-first-change
+```
+
+Open a pull request against **`master`** on `cppalliance/claude-code-chat-browser`. Include:
+
+- A short summary of **why** the change is needed.
+- A **Test plan** checklist (what you ran locally).
+- Links to any related issue (`Fixes #NNN` when applicable).
+
+### 7. Review
+
+[`.github/CODEOWNERS`](../.github/CODEOWNERS) auto-requests reviewers on new PRs. **Do not self-merge** — wait for at least one approval. Address review feedback in follow-up commits on the same branch.
+
+## Good first issues
+
+Browse open issues filtered by label:
+
+- [**good first issue**](https://github.com/cppalliance/claude-code-chat-browser/issues?q=is%3Aissue+is%3Aopen+label%3A%22good+first+issue%22) — scoped for newcomers
+- [**help wanted**](https://github.com/cppalliance/claude-code-chat-browser/issues?q=is%3Aissue+is%3Aopen+label%3A%22help+wanted%22) — maintainers welcome extra hands
+- [**documentation**](https://github.com/cppalliance/claude-code-chat-browser/issues?q=is%3Aissue+is%3Aopen+label%3Adocumentation) — docs-only patches
+
+Not sure which issue to pick? Comment on an issue or open a draft PR early for CI feedback — see [Getting help](../CONTRIBUTING.md#getting-help).
+
+## Maintainer coverage (bus factor)
+
+Recent commit history is concentrated on a small set of identities. If those maintainers are unavailable, review and release can stall.
+
+**Mitigations in this repo:**
+
+- **[`.github/CODEOWNERS`](../.github/CODEOWNERS)** — routes review requests so PRs do not rely on ad-hoc pings.
+- **This onboarding path** — lowers the ramp for a second reviewer or contributor to run gates and ship safely.
+
+If you are joining as a reviewer, read the [suggested reading order](#suggested-reading-order) and run the [full local gate](#5-run-the-full-local-gate) once on `master` before approving your first PR.