chore(agent): phase 15_agent_mtls from TODO.md (protected exporter web servers)

The single TODO item (exporters as protected web servers, certs as auth,
root certificate generated and managed by the collector) is now phase 15:
cert management in meta, agent TLS mode, https collector dials, gated
/api/certs surface, /certs admin page, installer + live rollout.

LLM-Generated: true

.agents/phases/todo/15_agent_mtls/01_cert_management.md

@@ -0,0 +1,43 @@
+# Task 01 — The dashboard owns a root CA and every cert it signs
+
+**Phase:** `15_agent_mtls` · **Source:** `TODO.md:3` — "I want all exporters to be protected web servers. The collector should generate and manage a root certificate that needs to be installed with each exporter. Use the certs as auth to each exporter."
+
+## Objective
+
+The certificate lifecycle becomes a pure, testable module: the dashboard generates a root CA once (idempotent across restarts), signs its own client cert and each agent's server cert, and supports reissue and revocation — all state in the `meta` table, exactly how `auth.py` keeps the verifier and the session secret.
+
+## Work
+
+1. `pyproject.toml` — add `cryptography` to `dependencies` (dashboard-side only; the agent stays stdlib-only) and run `uv lock`. Invariant 8: `uv pip list --outdated` empty afterwards.
+   - ASSUMPTION: `cryptography` is the only new dependency and it stays on the dashboard side; the agent (task 02) gains no third-party code — it loads the PEMs with stdlib `ssl`.
+2. `src/dashboards/certs.py` (new) — the whole lifecycle as pure functions over the three-method `MetaStore` protocol (the same protocol `auth.load_auth_state` uses, so this module imports nothing else from the package, and its tests use a dict):
+   - `ensure_certs(store, *, now: float | None = None)` → a frozen `CertsState` carrying the PEM text (`root_key`, `root_cert`, `client_key`, `client_cert`) plus the root/client `serial` + `not_after`. Reads the `meta` rows first; only generates and persists when missing (first boot); an existing row wins and is **never regenerated on restart** — regenerating on every start would rotate the CA and invalidate every installed agent bundle. `now` is injected (the module never reads a clock itself — the `auth.py` rule).
+   - meta keys (one concern per key, the `auth.*` precedent): `certs.root.key`, `certs.root.cert`, `certs.client.key`, `certs.client.cert`, `certs.agents` (one JSON object mapping `host name` → `{serial, not_after, status, bundle_rev, bundle, san}` — the bundle text is stored, so what the agent holds is byte-identical to what the API serves).
+   - Shapes: root CA self-signed, CN `dashboards-root`, **10 years**; client cert signed by the root, CN `dashboards`, **1 year**; agent server certs signed by the root, CN = the host name, **1 year**, `SAN` = the address(es) the dashboard dials for that host.
+     - ASSUMPTION: 10 y root / 1 y leaf lifetimes. No env seed for the root CA (unlike the admin password, the root key is a secret only the app needs to know, so it is auto-generated on first boot and merely persisted).
+   - `issue_agent_cert(store, state, name, san: list[str])` / `reissue_agent_cert(store, state, name, san)` — a fresh serial, `bundle_rev` +1 (1 on first issue), `status: "active"`, a fresh `bundle` (below). Idempotent per call — never issued on a read.
+   - `rotate_root(store, state)` — a fresh root CA + fresh client cert + every existing agent entry reissued (each `bundle_rev` +1): one action re-arms the whole fleet.
+   - `revoke(store, state, name)` — `status: "revoked"` (the serial stays on the denylist until a reissue gives the host a fresh identity; there is no "unrevoke" — reissue is the fix).
+   - the **bundle** (the install artifact, the TODO's "root certificate installed with each exporter"): one PEM text = the agent's server cert + the agent's key + the root CA *cert* (never the root key) + a `# BUNDLE-REV <n>` line + a `# REVOKED <serial>` line (one per revoked serial of the *current* root generation — a root rotation resets the list, since every cert is reissued anyway).
+   - ASSUMPTION: one client cert for the whole dashboard (the agent verifies "signed by our root", not a per-process identity); one agent entry per `HOST_TARGETS` name.
+   - invariant 6, the `auth.py` rule: no `logging` and no raise with anything interpolated — a malformed stored PEM is a fixed-text `RuntimeError` telling the operator to delete the `certs.*` meta keys (the shape of the auth reset), and nothing else.
+3. `src/dashboards/app.py` (+ the `AppContext` in `src/dashboards/api.py`) — the startup path builds `ctx.certs` (an `ensure_certs` read, the one-time bootstrap included) **before** `build_hub`, in both the owned-store (`build_context`) and the injected-store (lifespan) branches, through **one** helper so the two wiring sites cannot drift (the `build_hub` rule in AGENTS.md); the PEMs are written once to a private temp dir (mode `0600`, lives as long as the process) and the *paths* are what `AppContext.certs` carries for task 03's dialing.
+   - A `certs` whose stored PEM is malformed (a truncated `meta` row) is a fail-closed startup — a dashboard that cannot present its own credential must not start the loops (the `ctx.auth` rule, the one deliberate raise).
+
+## Testing & Quality
+
+- `tests/test_certs.py` (new) — a dict `MetaStore` (the `tests/test_auth.py` idiom):
+  - the first `ensure_certs` call persists exactly the five `certs.*` keys; the second is byte-identical (no regeneration — pin the `certs.root.cert` value);
+  - the parsed chain (`cryptography.x509` loaders) verifies: client → root, agent → root; the SAN list appears in the agent cert; the expiries match the assumed lifetimes (injected `now`);
+  - `reissue_agent_cert` bumps `serial` and `bundle_rev` and sets `status` active; `revoke` flips the status and puts the serial on the bundle's `# REVOKED` line; a reissue after a revoke gives a fresh serial that is *not* on the list;
+  - `rotate_root` reissues every agent entry (each `bundle_rev` bumped), the bundle carries the new root cert, and no stored value still contains the old root key;
+  - the bundle contains the agent cert + key + root cert + `# BUNDLE-REV` + the `# REVOKED` lines and **never** the root key (assert via the PEM header and a parsed-key mismatch);
+  - a malformed stored PEM → the fixed-text `RuntimeError` naming the meta keys, nothing interpolated.
+- Coverage: **>90%** on this task's new code.
+
+## Completion Criteria
+
+- [ ] `uv run pytest tests/test_certs.py` green; the full suite green
+- [ ] `uv pip list --outdated` empty; `uv run ruff check src tests agent` + `uv run pyright` clean
+- [ ] a fresh store boots with the `certs.*` rows present; a second boot changes no byte of `certs.root.cert`
+- [ ] no behaviour change in completed work: `auth.*` keys, the public surface, and the poller wiring are untouched