fix(security): server-authoritative approval gate + auth/session/file hardening

Remediate the HIGH and security-relevant findings from the 2026-07-11 audit.

H1 — the per-env approval gate is now server-authoritative. The governing
project is resolved from the target node's nearest-claimed ancestor
(`governing_env_policy`/`_tree` + `governing_project_id` +
`ProjectRepository::get_environments_by_id`), independent of the client-supplied
`[project]`. Omitting or spoofing the project block can no longer skip a gate the
owning project established; a to-create group resolves its declared parent's
chain so a fresh subtree node inherits the gate. Fails closed on any read error.

H2 — the API-key prefix slice (`&rest[..8]`) is now the boundary-safe
`rest.get(..8)`, so an attacker-supplied multibyte bearer can't panic the request
task (unauthenticated per-request DoS). Regression test added.

C1 — admin sessions gain an absolute lifetime cap (migration 0070,
`PICLOUD_SESSION_ABSOLUTE_TTL_HOURS`, default 30d): `lookup` filters it, `touch`
clamps the sliding bump to it, so a continuously-used or stolen-but-warm token
self-expires. Mirrors the data-plane app-user cap.

C2 — `Cache-Control: no-store` on the login and API-key-mint responses (the two
that return a raw credential), so a proxy/CDN/browser cache can't retain it.

B8 — file downloads are header-safe: `sanitize_stored_filename` guarantees a
valid `HeaderValue` (no panic on a control-char name) and BOTH the per-app and
group download paths now set attachment + `X-Content-Type-Options: nosniff` +
a restrictive CSP, closing a group-path stored-XSS gap.

Also folds in the server-side plan-warning plumbing (`plan_warnings`,
`PlanResult::warnings`) and the `app_only_reject` message helper that the CLI
plan-preview change builds on, plus operator security notes (reads-open shared-
topic SSE; the `--env` label is advisory, not a boundary).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/manager-core/tests/expected_schema.txt

@@ -19,6 +19,7 @@ table: admin_sessions
   created_at: timestamp with time zone NOT NULL default=now()
   expires_at: timestamp with time zone NOT NULL
   last_used_at: timestamp with time zone NOT NULL default=now()
+  absolute_expires_at: timestamp with time zone NOT NULL
 
 table: admin_users
   id: uuid NOT NULL default=gen_random_uuid()
@@ -474,6 +475,7 @@ indexes on abandoned_executions:
   idx_abandoned_executions_gc: public.abandoned_executions USING btree (created_at)
 
 indexes on admin_sessions:
+  admin_sessions_absolute_expiry_idx: public.admin_sessions USING btree (absolute_expires_at)
   admin_sessions_expiry_idx: public.admin_sessions USING btree (expires_at)
   admin_sessions_pkey: public.admin_sessions USING btree (token_hash)
   admin_sessions_user_idx: public.admin_sessions USING btree (user_id)
@@ -1035,3 +1037,4 @@ constraints on vars:
   0067: project environments
   0068: group dead letters
   0069: email secret version
+  0070: admin session absolute expiry

crates/manager-core/tests/projects_repo.rs

@@ -108,7 +108,7 @@ async fn list_with_owner_and_ancestors_surface_ownership() {
 #[tokio::test]
 async fn get_environments_by_slug_returns_persisted_policy() {
     // §3 M3 hermetic gate: the persisted per-env policy round-trips by project
-    // slug. Backs `ApplyService::effective_env_policy` (the `persisted` half).
+    // slug. Backs `ApplyService::governing_env_policy` (the `governing` half).
     let Some(pool) = pool_or_skip().await else {
         return;
     };
@@ -147,4 +147,15 @@ async fn get_environments_by_slug_returns_persisted_policy() {
         .await
         .expect("get_environments_by_slug");
     assert!(empty.is_empty());
+
+    // Audit 2026-07-11 H1: the gate now loads the policy by the SERVER-resolved
+    // project id (from the node's ownership walk), not the client slug. The
+    // by-id read must return the same persisted policy as the by-slug read.
+    let by_id = projects
+        .get_environments_by_id(proj_id.into())
+        .await
+        .expect("get_environments_by_id");
+    assert_eq!(by_id.get("production"), Some(&true));
+    assert_eq!(by_id.get("staging"), Some(&false));
+    assert_eq!(by_id.len(), 2);
 }