feat(harness): P1 — single registry-backed meta loader (rcust)

One loader: runner/harness/meta.py::load(recipe) -> RecipeMeta (frozen dataclass,
attribute access), backed by the declarative KEYS registry (14 final keys + 3
P2-deprecated). The ONLY exec() of tests/<recipe>/recipe_meta.py. Validation per
the locked decision: unknown ALL-CAPS top-level name or type mismatch = MetaError
(hard error at load); underscore-prefixed names recipe-private; callables only on
hook-typed keys.

Migrated all six legacy loaders (spec §4 L1–L6):
- run_recipe_ci.py::_load_meta deleted; orchestrator loads once, passes meta down
- tests/conftest.py::_recipe_meta deleted; meta fixture returns full RecipeMeta (R3)
- lifecycle.py::_recipe_extra_env/_recipe_meta_flag deleted; deploy_app takes meta
- deps.py::declared_deps deleted; callers read meta.DEPS
- canonical.py::is_enrolled reads through meta.load()
- screenshot.py now actually receives SCREENSHOT through the orchestrator path (R2
  fix; proven by unit test through the real load path)

Mumble private constants underscore-prefixed (_WELCOME_TEXT_MARKER/_MAX_USERS) +
importers fixed. New tests/unit/test_meta.py (all-recipes-load-clean typo gate,
MetaError cases, spec §2 baseline defaults, underscore exemption, doc sync). Docs
§4 key table now GENERATED from the registry (scripts/gen-meta-docs.py); drift
fails CI.

Verified on cc-ci: cc-ci-run -m pytest tests/unit -q -> 175 passed; scripts/lint.sh -> PASS.

runner/harness/deps.py

@@ -31,19 +31,7 @@ import os
 from collections.abc import Iterable
 
 from . import lifecycle, naming
-
-
-def declared_deps(recipe: str) -> list[str]:
-    """Read `DEPS` from `tests/<recipe>/recipe_meta.py` — a list of recipe names this recipe needs
-    deployed alongside it. Returns [] if none."""
-    path = os.path.join(os.path.dirname(__file__), "..", "..", "tests", recipe, "recipe_meta.py")
-    if not os.path.exists(path):
-        return []
-    ns: dict = {}
-    with open(path) as fh:
-        exec(compile(fh.read(), path, "exec"), ns)  # noqa: S102 (trusted, in-repo)
-    deps = ns.get("DEPS") or []
-    return [str(d) for d in deps if d]
+from . import meta as meta_mod
 
 
 def dep_domain(parent_recipe: str, pr: str, ref: str | None, dep_recipe: str) -> str:
@@ -81,11 +69,12 @@ def deploy_deps(
     pr: str,
     ref: str | None,
     deps: Iterable[str],
-    meta_for: dict[str, dict] | None = None,
+    meta_for: dict | None = None,
 ) -> list[dict]:
     """Deploy each declared dep, sequentially, at its per-run domain. Returns the list of state
-    dicts (one per dep). `meta_for` maps dep_recipe -> meta (HEALTH_PATH/HEALTH_OK/timeouts) so the
-    readiness wait uses per-dep config; missing dep meta falls back to (/, 200/301/302, 600s)."""
+    dicts (one per dep). `meta_for` maps dep_recipe -> RecipeMeta (HEALTH_PATH/HEALTH_OK/timeouts)
+    so the readiness wait uses per-dep config; a missing dep meta is loaded via meta.load()
+    (defaults: /, 200/301/302, 600s)."""
     meta_for = meta_for or {}
     state: list[dict] = []
     for dep in deps:
@@ -94,20 +83,21 @@ def deploy_deps(
         # NB: each dep_app gets a fresh deploy_count entry only on `_record_deploy` which fires
         # inside `lifecycle.deploy_app`. For Phase 2 the deploy-count guard (DG4.1) counts the
         # parent + its deps as distinct install events — by design, since each is a separate app.
-        dm = meta_for.get(dep, {})
+        dm = meta_for.get(dep) or meta_mod.load(dep)
         lifecycle.deploy_app(
             dep,
             domain,
             secrets=True,
-            deploy_timeout=int(dm.get("DEPLOY_TIMEOUT", 900)),
+            deploy_timeout=int(dm.DEPLOY_TIMEOUT),
+            meta=dm,
         )
         try:
             lifecycle.wait_healthy(
                 domain,
-                ok_codes=tuple(dm.get("HEALTH_OK", (200, 301, 302))),
-                path=dm.get("HEALTH_PATH", "/"),
-                deploy_timeout=int(dm.get("DEPLOY_TIMEOUT", 600)),
-                http_timeout=int(dm.get("HTTP_TIMEOUT", 600)),
+                ok_codes=tuple(dm.HEALTH_OK),
+                path=dm.HEALTH_PATH,
+                deploy_timeout=int(dm.DEPLOY_TIMEOUT),
+                http_timeout=int(dm.HTTP_TIMEOUT),
             )
         except Exception:
             # If a dep fails to converge, abort the whole resolve — let the caller teardown