Avoid duplicate config warnings for JSON consumers (#3190)

JSON config output already carries collected config diagnostics in warnings[], so prose stderr emission must be reserved for text/local paths. Lazy permission-mode default resolution prevents an earlier config load from leaking the same deprecation before the JSON renderer runs.\n\nConstraint: ROADMAP #815 requires text mode to keep human stderr warnings while JSON config/list suppresses duplicate app-level config prose.\nRejected: Filtering all stderr in JSON mode | would hide cargo/compiler or unrelated diagnostics outside the app config warning path.\nConfidence: high\nScope-risk: narrow\nDirective: Keep load_collecting_warnings side-effect-free; use load() for human stderr emission.\nTested: cargo fmt; cargo test -p rusty-claude-cli --test output_format_contract config_json_reports_deprecations_structurally_without_stderr_duplicate_815; cargo test -p rusty-claude-cli --test output_format_contract; manual target/debug/claw JSON config fixture.\nNot-tested: cargo clippy -p rusty-claude-cli --all-targets -- -D warnings is blocked by pre-existing runtime dead_code/trident warnings.

rust/crates/runtime/src/config.rs

@@ -379,12 +379,6 @@ impl ConfigLoader {
             loaded_entries.push(entry);
         }
 
-        // Still emit to stderr for non-JSON callers that go through the normal load() path;
-        // here we just *also* return them so callers can surface them structurally.
-        for warning in &all_warnings {
-            emit_config_warning_once(warning);
-        }
-
         let merged_value = JsonValue::Object(merged.clone());
 
         let feature_config = RuntimeFeatureConfig {

rust/crates/rusty-claude-cli/src/main.rs

@@ -1157,7 +1157,11 @@ fn parse_args(args: &[String]) -> Result<CliAction, String> {
         return action;
     }
 
-    let permission_mode = permission_mode_override.unwrap_or_else(default_permission_mode);
+    // Keep config-backed defaults lazy so pure-local JSON surfaces (notably
+    // `claw --output-format json config`) can report config warnings
+    // structurally without an earlier default-resolution load writing prose
+    // warnings to stderr.
+    let permission_mode = || permission_mode_override.unwrap_or_else(default_permission_mode);
 
     match rest[0].as_str() {
         "dump-manifests" => parse_dump_manifests_args(&rest[1..], output_format),
@@ -1301,7 +1305,7 @@ fn parse_args(args: &[String]) -> Result<CliAction, String> {
                     model,
                     output_format,
                     allowed_tools,
-                    permission_mode,
+                    permission_mode: permission_mode(),
                     compact,
                     base_commit,
                     reasoning_effort: reasoning_effort.clone(),
@@ -1338,7 +1342,7 @@ fn parse_args(args: &[String]) -> Result<CliAction, String> {
                 model,
                 output_format,
                 allowed_tools,
-                permission_mode,
+                permission_mode: permission_mode(),
                 compact,
                 base_commit: base_commit.clone(),
                 reasoning_effort: reasoning_effort.clone(),
@@ -1350,7 +1354,7 @@ fn parse_args(args: &[String]) -> Result<CliAction, String> {
             model,
             output_format,
             allowed_tools,
-            permission_mode,
+            permission_mode(),
             compact,
             base_commit,
             reasoning_effort,
@@ -1389,7 +1393,7 @@ fn parse_args(args: &[String]) -> Result<CliAction, String> {
                 model,
                 output_format,
                 allowed_tools,
-                permission_mode,
+                permission_mode: permission_mode(),
                 compact,
                 base_commit,
                 reasoning_effort: reasoning_effort.clone(),

rust/crates/rusty-claude-cli/tests/output_format_contract.rs

@@ -1259,6 +1259,66 @@ fn inventory_commands_deduplicate_config_deprecation_warnings_per_process() {
     }
 }
 
+#[test]
+fn config_json_reports_deprecations_structurally_without_stderr_duplicate_815() {
+    let root = unique_temp_dir("config-json-warning-815");
+    let config_home = root.join("config-home");
+    let home = root.join("home");
+    fs::create_dir_all(&config_home).expect("config home should exist");
+    fs::create_dir_all(&home).expect("home should exist");
+    fs::write(
+        config_home.join("settings.json"),
+        r#"{"enabledPlugins": {}}"#,
+    )
+    .expect("deprecated config fixture should write");
+
+    let envs = [
+        (
+            "CLAW_CONFIG_HOME",
+            config_home.to_str().expect("utf8 config home"),
+        ),
+        ("HOME", home.to_str().expect("utf8 home")),
+    ];
+    let output = run_claw(&root, &["--output-format", "json", "config"], &envs);
+    assert!(
+        output.status.success(),
+        "stdout:\n{}\n\nstderr:\n{}",
+        String::from_utf8_lossy(&output.stdout),
+        String::from_utf8_lossy(&output.stderr)
+    );
+
+    let parsed: Value =
+        serde_json::from_slice(&output.stdout).expect("stdout should be valid json");
+    let warnings = parsed["warnings"]
+        .as_array()
+        .expect("config JSON should include warnings[]");
+    assert!(
+        warnings.iter().any(|warning| warning
+            .as_str()
+            .is_some_and(|text| text.contains("field \"enabledPlugins\" is deprecated"))),
+        "config JSON warnings[] should include enabledPlugins deprecation: {parsed}"
+    );
+
+    let stderr = String::from_utf8(output.stderr).expect("stderr utf8");
+    assert!(
+        !stderr.contains("field \"enabledPlugins\" is deprecated"),
+        "JSON config should not duplicate collected config deprecations on stderr:\n{stderr}"
+    );
+
+    let text_output = run_claw(&root, &["config"], &envs);
+    assert!(
+        text_output.status.success(),
+        "stdout:\n{}\n\nstderr:\n{}",
+        String::from_utf8_lossy(&text_output.stdout),
+        String::from_utf8_lossy(&text_output.stderr)
+    );
+    let text_stderr = String::from_utf8(text_output.stderr).expect("stderr utf8");
+    assert!(
+        text_stderr.contains("field \"enabledPlugins\" is deprecated"),
+        "text config should keep human-readable config warnings on stderr"
+    );
+}
+
 fn assert_json_command(current_dir: &Path, args: &[&str]) -> Value {
     assert_json_command_with_env(current_dir, args, &[])
 }