Make plan approval gate only active in plan mode

- Add in_plan_mode flag to Agent struct
- Add set_plan_mode() and is_plan_mode() methods
- Gate check now only runs when in_plan_mode is true
- CLI calls set_plan_mode(true) on /plan command and EnterPlanMode
- CLI calls set_plan_mode(false) on approval and CTRL-D exit
- Update integration test to enable plan mode
- Fix test YAML to use Vec<Check> for negative/boundary checks

crates/g3-cli/src/interactive.rs

@@ -415,6 +415,7 @@ pub async fn run_interactive<W: UiWriter>(
                         if approved {
                             // Exit plan mode on successful approval
                             in_plan_mode = false;
+                            agent.set_plan_mode(false);
                             
                             // Add synthetic assistant message so LLM knows plan was approved
                             use g3_providers::{Message, MessageRole};
@@ -448,6 +449,7 @@ pub async fn run_interactive<W: UiWriter>(
                             }
                             CommandResult::EnterPlanMode => {
                                 in_plan_mode = true;
+                                agent.set_plan_mode(true);
                                 continue;
                             }
                         }
@@ -480,6 +482,7 @@ pub async fn run_interactive<W: UiWriter>(
                 if in_plan_mode {
                     output.print("CTRL-D (exiting plan mode)");
                     in_plan_mode = false;
+                    agent.set_plan_mode(false);
                     // Continue the loop with normal prompt
                     continue;
                 } else {

crates/g3-core/src/lib.rs

@@ -155,6 +155,8 @@ pub struct Agent<W: UiWriter> {
     auto_memory: bool,
     /// Whether aggressive context dehydration is enabled (--acd flag)
     acd_enabled: bool,
+    /// Whether plan mode is active (gate blocks file changes without approved plan)
+    in_plan_mode: bool,
     /// Manager for async research tasks
     pending_research_manager: pending_research::PendingResearchManager,
 }
@@ -210,6 +212,7 @@ impl<W: UiWriter> Agent<W> {
             agent_name: None,
             auto_memory: false,
             acd_enabled: false,
+            in_plan_mode: false,
             pending_research_manager: pending_research::PendingResearchManager::new(),
         }
     }
@@ -1609,6 +1612,16 @@ impl<W: UiWriter> Agent<W> {
         );
     }
 
+    /// Enable or disable plan mode (blocks file changes without approved plan)
+    pub fn set_plan_mode(&mut self, enabled: bool) {
+        self.in_plan_mode = enabled;
+    }
+
+    /// Check if plan mode is active
+    pub fn is_plan_mode(&self) -> bool {
+        self.in_plan_mode
+    }
+
     // =========================================================================
     // STREAMING & LLM INTERACTION
     // =========================================================================
@@ -2901,7 +2914,8 @@ Skip if nothing new. Be brief."#;
 
         let result = self.execute_tool_inner_in_dir(tool_call, working_dir).await;
 
-        // Check plan approval gate after tool execution
+        // Check plan approval gate after tool execution (only in plan mode)
+        if self.in_plan_mode {
             if let Some(session_id) = &self.session_id {
             if let ApprovalGateResult::Blocked { message, .. } = 
                 check_plan_approval_gate(session_id, working_dir) 
@@ -2910,6 +2924,7 @@ Skip if nothing new. Be brief."#;
                 return Ok(message);
             }
             }
+        }
 
         let log_str = match &result {
             Ok(s) => s.clone(),

crates/g3-core/tests/mock_provider_integration_test.rs

@@ -906,6 +906,9 @@ async fn test_plan_approval_gate_blocks_unapproved_changes() {
     // Set the working directory to the temp git repo
     agent.set_working_dir(temp_path.to_string_lossy().to_string());
     
+    // Enable plan mode (required for the gate check to run)
+    agent.set_plan_mode(true);
+    
     // Create an unapproved plan for this session
     let mut plan = Plan::new("test-plan");
     plan.items.push(PlanItem {
@@ -915,8 +918,8 @@ async fn test_plan_approval_gate_blocks_unapproved_changes() {
         touches: vec!["src/test.rs".to_string()],
         checks: Checks {
             happy: Check::new("happy", "target"),
-            negative: Check::new("negative", "target"),
-            boundary: Check::new("boundary", "target"),
+            negative: vec![Check::new("negative", "target")],
+            boundary: vec![Check::new("boundary", "target")],
         },
         evidence: vec![],
         notes: None,

crates/g3-core/tests/stream_completion_characterization_test.rs

@@ -616,10 +616,10 @@ items:
         desc: Works correctly
         target: test::module
       negative:
-        desc: Handles errors
+        - desc: Handles errors
           target: test::module
       boundary:
-        desc: Edge cases
+        - desc: Edge cases
           target: test::module"#
             }),
         };

crates/g3-core/tests/tool_execution_roundtrip_test.rs

@@ -420,10 +420,10 @@ items:
         desc: Works
         target: test
       negative:
-        desc: Errors
+        - desc: Errors
           target: test
       boundary:
-        desc: Edge
+        - desc: Edge
           target: test"#
             }),
         );
@@ -477,8 +477,8 @@ items:
     touches: ["src/test.rs"]
     checks:
       happy: {desc: Works, target: test}
-      negative: {desc: Errors, target: test}
-      boundary: {desc: Edge, target: test}"#
+      negative: [{desc: Errors, target: test}]
+      boundary: [{desc: Edge, target: test}]"#
             }),
         );
         agent.execute_tool(&write_call).await.unwrap();