docs: Expand AGENTS.md with coding agents guidance (#1392)

* Expand AGENTS.md with repo guidance for coding agents

* Format AGENTS deeper docs as a multiline list

* Move scoping guidance to change-discipline section

* Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <[email protected]>

* Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <[email protected]>

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Co-authored-by: Copilot Autofix powered by AI <[email protected]>

AGENTS.md

@@ -1,6 +1,94 @@
 # Agent Rules
 
-## Feature Parity Update Policy
+## Purpose and Precedence
 
+- `AGENTS.md` is the quick-start contract for coding agents. It is not the full architecture spec.
+- Read the relevant subsystem spec before changing a complex area. When a repo spec exists, treat it as authoritative.
+Start with these deeper docs as needed:
+- `CLAUDE.md`
+- `src/agent/CLAUDE.md`
+- `src/channels/web/CLAUDE.md`
+- `src/db/CLAUDE.md`
+- `src/llm/CLAUDE.md`
+- `src/setup/README.md`
+- `src/tools/README.md`
+- `src/workspace/README.md`
+- `src/NETWORK_SECURITY.md`
+- `tests/e2e/CLAUDE.md`
+
+## Architecture Mental Model
+
+- Channels normalize external input into `IncomingMessage`; `ChannelManager` merges all active channel streams.
+- `Agent` owns session/thread/turn handling, submission parsing, the LLM/tool loop, approvals, routines, and background runtime behavior.
+- `AppBuilder` is the composition root that wires database, secrets, LLMs, tools, workspace, extensions, skills, hooks, and cost controls before the agent starts.
+- The web gateway is a browser-facing API/UI layered on top of the same agent/session/tool systems, not a separate product path.
+
+## Where to Work
+
+- Agent/runtime behavior: `src/agent/`
+- Web gateway/API/SSE/WebSocket: `src/channels/web/`
+- Persistence and DB abstractions: `src/db/`
+- Setup/onboarding/configuration flow: `src/setup/`
+- LLM providers and routing: `src/llm/`
+- Workspace, memory, embeddings, search: `src/workspace/`
+- Extensions, tools, channels, MCP, WASM: `src/extensions/`, `src/tools/`, `src/channels/`
+
+## Ownership and Composition Rules
+
+- Keep `src/main.rs` and `src/app.rs` orchestration-focused. Do not move module-owned logic into entrypoints.
+- Module-specific initialization should live in the owning module behind a public factory/helper, not be reimplemented ad hoc.
+- Keep feature-flag branching inside the module that owns the abstraction whenever possible.
+- Prefer extending existing traits and registries over hardcoding one-off integration paths.
+
+## Repo-Wide Coding Rules
+
+- Avoid `.unwrap()` and `.expect()` in production; prefer proper error handling. They are fine in tests, and in production only for truly infallible invariants (e.g., literals/regexes) with a safety comment.
+- Keep clippy clean with zero warnings.
+- Prefer `crate::` imports for cross-module references.
+- Use strong types and enums over stringly-typed control flow when the shape is known.
+
+## Database, Setup, and Config Rules
+
+- New persistence behavior must support both PostgreSQL and libSQL.
+- Add new DB operations to the shared DB trait first, then implement both backends.
+- Treat bootstrap config, DB-backed settings, and encrypted secrets as distinct layers; do not collapse them casually.
+- If onboarding or setup behavior changes, update `src/setup/README.md` in the same branch.
+- Do not break config precedence, bootstrap env loading, DB-backed config reload, or post-secrets LLM re-resolution.
+
+## Security and Runtime Invariants
+
+- Review any change touching listeners, routes, auth, secrets, sandboxing, approvals, or outbound HTTP with a security mindset.
+- Do not weaken bearer-token auth, webhook auth, CORS/origin checks, body limits, rate limits, allowlists, or secret-handling guarantees.
+- Treat Docker containers and external services as untrusted.
+- Session/thread/turn state matters. Submission parsing happens before normal chat handling.
+- Skills are selected deterministically. Tool approval and auth flows are special paths and must not be mixed into normal chat history carelessly.
+- Persistent memory is the workspace system, not just transcript storage; preserve file-like semantics, chunking/search behavior, and identity/system-prompt loading.
+
+## Tools, Channels, and Extensions
+
+- Use a built-in Rust tool for core internal capabilities tightly coupled to the runtime.
+- Use WASM tools or WASM channels for sandboxed extensions and plugin-style integrations.
+- Use MCP for external server integrations when the capability belongs outside the main binary.
+- Preserve extension lifecycle expectations: install, authenticate/configure, activate, remove.
+
+## Docs, Parity, and Testing
+
+- If behavior changes, update the relevant docs/specs in the same branch.
 - If you change implementation status for any feature tracked in `FEATURE_PARITY.md`, update that file in the same branch.
 - Do not open a PR that changes feature behavior without checking `FEATURE_PARITY.md` for needed status updates (`❌`, `🚧`, `✅`, notes, and priorities).
+- Add the narrowest tests that validate the change: unit tests for local logic, integration tests for runtime/DB/routing behavior, and E2E or trace coverage for gateway, approvals, extensions, or other user-visible flows.
+
+## Risk and Change Discipline
+
+- Keep changes scoped; avoid broad refactors unless the task truly requires them.
+- Security, database schema, runtime, worker, CI, and secrets changes are high-risk. Call out rollback risks, compatibility concerns, and hidden side effects.
+- Preserve existing defaults unless the task explicitly changes them.
+- Avoid unrelated file churn and generated-file edits unless required.
+- Respect a dirty worktree and never revert user changes you did not make.
+
+## Before Finishing
+
+- Confirm whether behavior changes require updates to `FEATURE_PARITY.md`, specs, API docs, or `CHANGELOG.md`.
+- Run the most targeted tests/checks that cover the change.
+- Re-check security-sensitive paths when touching auth, secrets, network listeners, sandboxing, or approvals.
+- Keep the final diff scoped to the task.