Marketplace sync: keep installs the host could not build (final review M3)

An install the host skipped (pinned commit missing from the cache, cache
unreadable, item failing a tightened validation rule) never reached the
manifest, so sync.sh treated it as deselected and deleted it from the
container. The manifest now carries `held`: the state ids of such
installs ("plugin:<slug>/<key>" for plugins). The script counts them as
still selected and carries their records forward, as it already does
for items that fail inside the container. A removed marketplace is the
one skip that still removes; a malformed `held` list changes nothing.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/src-tauri/src/marketplace/sync_script_tests.rs

@@ -1057,3 +1057,90 @@ fn a_slug_change_reinstalls_under_the_new_name_and_retires_the_old() {
     let r = run(&env);
     assert!(nothing_reported(&r), "{r:?}");
 }
+
+// ── Host-side holds (final review M3) ────────────────────────────────────────
+
+/// Everything `install_all` installed, plus plugin `p` from SLUG_A.
+fn install_all_and_a_plugin(env: &Env) {
+    let (base, mut manifest) = all_kinds(C1);
+    let mut files: Vec<(String, String, bool)> = base
+        .iter()
+        .map(|(p, t, e)| (p.to_string(), t.to_string(), *e))
+        .collect();
+    files.push((
+        format!("plugins/{SLUG_A}/.claude-plugin/marketplace.json"),
+        format!(
+            r#"{{"name":"triple-c-{SLUG_A}","owner":{{"name":"Triple-C"}},"plugins":[{{"name":"p","source":"./p"}}]}}"#
+        ),
+        false,
+    ));
+    files.push((
+        format!("plugins/{SLUG_A}/p/.claude-plugin/plugin.json"),
+        r#"{"name":"p"}"#.to_string(),
+        false,
+    ));
+    manifest["items"].as_array_mut().unwrap().push(
+        json!({ "kind": "plugin", "key": "p", "marketplace": "m1", "commit": C1, "slug": SLUG_A }),
+    );
+    manifest["plugin_marketplaces"] =
+        json!([{ "slug": SLUG_A, "dir": format!("plugins/{SLUG_A}"), "plugins": ["p"] }]);
+    let refs: Vec<(&str, &str, bool)> = files
+        .iter()
+        .map(|(p, t, e)| (p.as_str(), t.as_str(), *e))
+        .collect();
+    payload(env, &refs, manifest);
+    let r = run(env);
+    assert_eq!(r.installed.len(), 5, "{r:?}");
+}
+
+#[test]
+fn held_items_are_kept_not_removed() {
+    let Some(env) = env() else { return };
+    install_all_and_a_plugin(&env);
+    let settings_path = env.home.join(".claude/settings.json");
+    let state_path = env.home.join(".claude/triple-c/marketplace/state.json");
+    let state_before = read_json(&state_path)["items"].clone();
+
+    // The host could build none of them this time (cache gone, say).
+    fs::remove_file(&env.log).unwrap();
+    let mut manifest = empty_manifest();
+    manifest["held"] = json!([
+        "agent:code-reviewer",
+        "skill:example-skill",
+        "command:example-command",
+        "hook:notify-on-stop",
+        format!("plugin:{SLUG_A}/p"),
+    ]);
+    payload(&env, &[], manifest);
+    let r = run(&env);
+
+    assert!(nothing_reported(&r), "{r:?}");
+    assert_all_installed(&env);
+    assert!(claude_log(&env).is_empty(), "{:?}", claude_log(&env));
+    assert_eq!(read_json(&settings_path)["hooks"], hook_settings());
+    assert_eq!(read_json(&state_path)["items"], state_before);
+    assert!(env
+        .home
+        .join(format!(".claude/triple-c/plugins/{SLUG_A}"))
+        .is_dir());
+
+    // A real deselection afterwards still removes everything.
+    payload(&env, &[], empty_manifest());
+    let r = run(&env);
+    assert_eq!(r.removed.len(), 5, "{r:?}");
+}
+
+#[test]
+fn a_malformed_held_list_changes_nothing() {
+    let Some(env) = env() else { return };
+    install_all(&env);
+    for bad in [json!("agent:code-reviewer"), json!([1]), json!({})] {
+        let mut manifest = empty_manifest();
+        manifest["held"] = bad.clone();
+        payload(&env, &[], manifest);
+        let r = run(&env);
+        assert!(r.removed.is_empty(), "{bad}: {r:?}");
+        assert_eq!(r.errors.len(), 1, "{bad}: {r:?}");
+        assert_all_installed(&env);
+    }
+}