feat: make AI chat tool use blocks expandable with input/output details

Tool call blocks in AI Chat are now clickable and expandable to show
tool name, input parameters (pretty-printed JSON), and output/result.
Collapsed by default, keyboard accessible (Tab/Enter/Space/Esc).

Backend: Rust stream events now carry tool input (accumulated from
input_json_delta chunks) and tool output (from tool_result events).
Frontend: AiActionCard is a disclosure widget with aria-expanded,
error output shown in red, long content truncated.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src-tauri/src/claude_cli.rs

@@ -1,4 +1,5 @@
 use serde::{Deserialize, Serialize};
+use std::collections::HashMap;
 use std::io::BufRead;
 use std::path::PathBuf;
 use std::process::{Command, Stdio};
@@ -19,9 +20,18 @@ pub enum ClaudeStreamEvent {
     /// Incremental text chunk.
     TextDelta { text: String },
     /// A tool call started (agent mode only).
-    ToolStart { tool_name: String, tool_id: String },
+    ToolStart {
+        tool_name: String,
+        tool_id: String,
+        #[serde(skip_serializing_if = "Option::is_none")]
+        input: Option<String>,
+    },
     /// A tool call finished (agent mode only).
-    ToolDone { tool_id: String },
+    ToolDone {
+        tool_id: String,
+        #[serde(skip_serializing_if = "Option::is_none")]
+        output: Option<String>,
+    },
     /// Final result text + session ID.
     Result { text: String, session_id: String },
     /// Something went wrong.
@@ -207,6 +217,15 @@ fn build_mcp_config(vault_path: &str) -> Result<String, String> {
     serde_json::to_string(&config).map_err(|e| format!("Failed to serialise MCP config: {e}"))
 }
 
+/// Mutable state accumulated across the JSON stream for a single subprocess.
+struct StreamState {
+    session_id: String,
+    /// Accumulates `input_json_delta` chunks keyed by tool_use id.
+    tool_inputs: HashMap<String, String>,
+    /// The tool_use id of the block currently being streamed.
+    current_tool_id: Option<String>,
+}
+
 /// Core subprocess runner shared by chat and agent modes.
 fn run_claude_subprocess<F>(bin: &PathBuf, args: &[String], emit: &mut F) -> Result<String, String>
 where
@@ -223,7 +242,11 @@ where
     let stdout = child.stdout.take().ok_or("No stdout handle")?;
     let reader = std::io::BufReader::new(stdout);
 
-    let mut session_id = String::new();
+    let mut state = StreamState {
+        session_id: String::new(),
+        tool_inputs: HashMap::new(),
+        current_tool_id: None,
+    };
 
     for line in reader.lines() {
         let line = match line {
@@ -245,7 +268,7 @@ where
             Err(_) => continue, // skip non-JSON lines
         };
 
-        dispatch_event(&json, &mut session_id, emit);
+        dispatch_event(&json, &mut state, emit);
     }
 
     // Read stderr for potential error messages.
@@ -257,7 +280,7 @@ where
 
     let status = child.wait().map_err(|e| format!("Wait failed: {e}"))?;
 
-    if !status.success() && session_id.is_empty() {
+    if !status.success() && state.session_id.is_empty() {
         let msg = if stderr_output.contains("not logged in")
             || stderr_output.contains("authentication")
             || stderr_output.contains("auth")
@@ -273,11 +296,11 @@ where
 
     emit(ClaudeStreamEvent::Done);
 
-    Ok(session_id)
+    Ok(state.session_id)
 }
 
 /// Parse a single JSON line from the stream and emit the appropriate event.
-fn dispatch_event<F>(json: &serde_json::Value, session_id: &mut String, emit: &mut F)
+fn dispatch_event<F>(json: &serde_json::Value, state: &mut StreamState, emit: &mut F)
 where
     F: FnMut(ClaudeStreamEvent),
 {
@@ -287,7 +310,7 @@ where
         // --- System init → capture session_id ---
         "system" if json["subtype"].as_str() == Some("init") => {
             if let Some(sid) = json["session_id"].as_str() {
-                *session_id = sid.to_string();
+                state.session_id = sid.to_string();
                 emit(ClaudeStreamEvent::Init {
                     session_id: sid.to_string(),
                 });
@@ -296,7 +319,7 @@ where
 
         // --- Streaming partial events (text deltas, tool_use starts) ---
         "stream_event" => {
-            dispatch_stream_event(json, emit);
+            dispatch_stream_event(json, state, emit);
         }
 
         // --- Tool progress (agent mode) ---
@@ -307,6 +330,18 @@ where
                 emit(ClaudeStreamEvent::ToolStart {
                     tool_name: name.to_string(),
                     tool_id: id.to_string(),
+                    input: None,
+                });
+            }
+        }
+
+        // --- Tool result (agent mode) ---
+        "tool_result" => {
+            if let Some(id) = json["tool_use_id"].as_str() {
+                let output = extract_tool_result_text(json);
+                emit(ClaudeStreamEvent::ToolDone {
+                    tool_id: id.to_string(),
+                    output,
                 });
             }
         }
@@ -315,7 +350,7 @@ where
         "result" => {
             let sid = json["session_id"].as_str().unwrap_or("").to_string();
             if !sid.is_empty() {
-                *session_id = sid.clone();
+                state.session_id = sid.clone();
             }
             let text = json["result"].as_str().unwrap_or("").to_string();
             emit(ClaudeStreamEvent::Result {
@@ -332,9 +367,11 @@ where
                         if let (Some(id), Some(name)) =
                             (block["id"].as_str(), block["name"].as_str())
                         {
+                            let input = format_tool_input(&block["input"], state, id);
                             emit(ClaudeStreamEvent::ToolStart {
                                 tool_name: name.to_string(),
                                 tool_id: id.to_string(),
+                                input,
                             });
                         }
                     }
@@ -347,7 +384,7 @@ where
 }
 
 /// Handle a `stream_event` (partial assistant message).
-fn dispatch_stream_event<F>(json: &serde_json::Value, emit: &mut F)
+fn dispatch_stream_event<F>(json: &serde_json::Value, state: &mut StreamState, emit: &mut F)
 where
     F: FnMut(ClaudeStreamEvent),
 {
@@ -357,29 +394,87 @@ where
     match event_type {
         "content_block_delta" => {
             let delta = &event["delta"];
-            if delta["type"].as_str() == Some("text_delta") {
-                if let Some(text) = delta["text"].as_str() {
-                    emit(ClaudeStreamEvent::TextDelta {
-                        text: text.to_string(),
-                    });
+            match delta["type"].as_str() {
+                Some("text_delta") => {
+                    if let Some(text) = delta["text"].as_str() {
+                        emit(ClaudeStreamEvent::TextDelta {
+                            text: text.to_string(),
+                        });
+                    }
                 }
+                Some("input_json_delta") => {
+                    if let (Some(partial), Some(ref tid)) =
+                        (delta["partial_json"].as_str(), &state.current_tool_id)
+                    {
+                        state
+                            .tool_inputs
+                            .entry(tid.clone())
+                            .or_default()
+                            .push_str(partial);
+                    }
+                }
+                _ => {}
             }
         }
         "content_block_start" => {
             let block = &event["content_block"];
             if block["type"].as_str() == Some("tool_use") {
                 if let (Some(id), Some(name)) = (block["id"].as_str(), block["name"].as_str()) {
+                    state.current_tool_id = Some(id.to_string());
+                    state.tool_inputs.entry(id.to_string()).or_default();
                     emit(ClaudeStreamEvent::ToolStart {
                         tool_name: name.to_string(),
                         tool_id: id.to_string(),
+                        input: None,
                     });
                 }
             }
         }
+        "content_block_stop" => {
+            state.current_tool_id = None;
+        }
         _ => {}
     }
 }
 
+/// Build the tool input string, preferring accumulated delta chunks over the
+/// block's `input` field (which may be empty at stream start).
+fn format_tool_input(
+    block_input: &serde_json::Value,
+    state: &StreamState,
+    tool_id: &str,
+) -> Option<String> {
+    if let Some(accumulated) = state.tool_inputs.get(tool_id) {
+        if !accumulated.is_empty() {
+            return Some(accumulated.clone());
+        }
+    }
+    if !block_input.is_null() && block_input.as_object().is_some_and(|o| !o.is_empty()) {
+        return Some(block_input.to_string());
+    }
+    None
+}
+
+/// Extract displayable text from a `tool_result` event.
+fn extract_tool_result_text(json: &serde_json::Value) -> Option<String> {
+    // String content field
+    if let Some(s) = json["content"].as_str() {
+        return Some(s.to_string());
+    }
+    // Array of content blocks (Claude format)
+    if let Some(arr) = json["content"].as_array() {
+        let texts: Vec<&str> = arr
+            .iter()
+            .filter_map(|b| b["text"].as_str())
+            .collect();
+        if !texts.is_empty() {
+            return Some(texts.join("\n"));
+        }
+    }
+    // Fallback: "output" field
+    json["output"].as_str().map(|s| s.to_string())
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -408,12 +503,20 @@ mod tests {
 
     // --- dispatch_event / dispatch_stream_event ---
 
+    fn new_state() -> StreamState {
+        StreamState {
+            session_id: String::new(),
+            tool_inputs: HashMap::new(),
+            current_tool_id: None,
+        }
+    }
+
     /// Run dispatch_event on the given JSON and return (session_id, events).
     fn run_dispatch(json: serde_json::Value) -> (String, Vec<ClaudeStreamEvent>) {
-        let mut sid = String::new();
+        let mut state = new_state();
         let mut events = vec![];
-        dispatch_event(&json, &mut sid, &mut |e| events.push(e));
-        (sid, events)
+        dispatch_event(&json, &mut state, &mut |e| events.push(e));
+        (state.session_id, events)
     }
 
     /// Run dispatch_event with a pre-set session_id.
@@ -421,10 +524,23 @@ mod tests {
         json: serde_json::Value,
         initial_sid: &str,
     ) -> (String, Vec<ClaudeStreamEvent>) {
-        let mut sid = initial_sid.to_string();
+        let mut state = new_state();
+        state.session_id = initial_sid.to_string();
         let mut events = vec![];
-        dispatch_event(&json, &mut sid, &mut |e| events.push(e));
-        (sid, events)
+        dispatch_event(&json, &mut state, &mut |e| events.push(e));
+        (state.session_id, events)
+    }
+
+    /// Run multiple dispatch_event calls sharing state (for multi-event sequences).
+    fn run_dispatch_sequence(
+        events_json: Vec<serde_json::Value>,
+    ) -> (StreamState, Vec<ClaudeStreamEvent>) {
+        let mut state = new_state();
+        let mut events = vec![];
+        for json in &events_json {
+            dispatch_event(json, &mut state, &mut |e| events.push(e));
+        }
+        (state, events)
     }
 
     #[test]
@@ -468,7 +584,7 @@ mod tests {
             "event": { "type": "content_block_start", "index": 1, "content_block": { "type": "tool_use", "id": "tool_abc", "name": "read_note", "input": {} } }
         }));
         assert!(
-            matches!(&events[0], ClaudeStreamEvent::ToolStart { tool_name, tool_id } if tool_name == "read_note" && tool_id == "tool_abc")
+            matches!(&events[0], ClaudeStreamEvent::ToolStart { tool_name, tool_id, .. } if tool_name == "read_note" && tool_id == "tool_abc")
         );
     }
 
@@ -501,7 +617,7 @@ mod tests {
             "type": "tool_progress", "tool_name": "search_notes", "tool_use_id": "tool_xyz"
         }));
         assert!(
-            matches!(&events[0], ClaudeStreamEvent::ToolStart { tool_name, tool_id } if tool_name == "search_notes" && tool_id == "tool_xyz")
+            matches!(&events[0], ClaudeStreamEvent::ToolStart { tool_name, tool_id, .. } if tool_name == "search_notes" && tool_id == "tool_xyz")
         );
     }
 
@@ -523,7 +639,7 @@ mod tests {
         }));
         assert_eq!(events.len(), 1);
         assert!(
-            matches!(&events[0], ClaudeStreamEvent::ToolStart { tool_name, tool_id } if tool_name == "search_notes" && tool_id == "tu_1")
+            matches!(&events[0], ClaudeStreamEvent::ToolStart { tool_name, tool_id, .. } if tool_name == "search_notes" && tool_id == "tu_1")
         );
     }
 
@@ -541,7 +657,8 @@ mod tests {
     }
 
     #[test]
-    fn dispatch_stream_event_non_text_delta_is_ignored() {
+    fn dispatch_stream_event_input_json_delta_accumulates_silently() {
+        // input_json_delta doesn't emit events directly — it accumulates in state
         let (_, events) = run_dispatch(serde_json::json!({
             "type": "stream_event",
             "event": { "type": "content_block_delta", "index": 0, "delta": { "type": "input_json_delta", "partial_json": "{}" } }
@@ -566,6 +683,109 @@ mod tests {
         assert!(events.is_empty());
     }
 
+    #[test]
+    fn dispatch_event_handles_tool_result_string_content() {
+        let (_, events) = run_dispatch(serde_json::json!({
+            "type": "tool_result",
+            "tool_use_id": "tool_abc",
+            "content": "Found 3 notes matching query"
+        }));
+        assert_eq!(events.len(), 1);
+        assert!(
+            matches!(&events[0], ClaudeStreamEvent::ToolDone { tool_id, output }
+                if tool_id == "tool_abc" && output.as_deref() == Some("Found 3 notes matching query"))
+        );
+    }
+
+    #[test]
+    fn dispatch_event_handles_tool_result_array_content() {
+        let (_, events) = run_dispatch(serde_json::json!({
+            "type": "tool_result",
+            "tool_use_id": "tool_def",
+            "content": [{ "type": "text", "text": "Line 1" }, { "type": "text", "text": "Line 2" }]
+        }));
+        assert!(
+            matches!(&events[0], ClaudeStreamEvent::ToolDone { output, .. }
+                if output.as_deref() == Some("Line 1\nLine 2"))
+        );
+    }
+
+    #[test]
+    fn dispatch_event_tool_result_missing_tool_id_is_ignored() {
+        let (_, events) = run_dispatch(serde_json::json!({
+            "type": "tool_result", "content": "result text"
+        }));
+        assert!(events.is_empty());
+    }
+
+    #[test]
+    fn dispatch_accumulates_input_json_deltas() {
+        let (_, events) = run_dispatch_sequence(vec![
+            // Start tool_use block
+            serde_json::json!({
+                "type": "stream_event",
+                "event": { "type": "content_block_start", "content_block": { "type": "tool_use", "id": "t1", "name": "search_notes", "input": {} } }
+            }),
+            // Input delta chunks
+            serde_json::json!({
+                "type": "stream_event",
+                "event": { "type": "content_block_delta", "delta": { "type": "input_json_delta", "partial_json": "{\"query\":" } }
+            }),
+            serde_json::json!({
+                "type": "stream_event",
+                "event": { "type": "content_block_delta", "delta": { "type": "input_json_delta", "partial_json": "\"test\"}" } }
+            }),
+            // Stop block
+            serde_json::json!({
+                "type": "stream_event",
+                "event": { "type": "content_block_stop" }
+            }),
+            // Assistant message triggers ToolStart with accumulated input
+            serde_json::json!({
+                "type": "assistant",
+                "message": { "content": [
+                    { "type": "tool_use", "id": "t1", "name": "search_notes", "input": { "query": "test" } }
+                ] }
+            }),
+        ]);
+        // First event: ToolStart with no input (from content_block_start)
+        assert!(matches!(&events[0], ClaudeStreamEvent::ToolStart { input: None, .. }));
+        // Second event: ToolStart with accumulated input (from assistant)
+        assert!(
+            matches!(&events[1], ClaudeStreamEvent::ToolStart { input: Some(inp), .. }
+                if inp == "{\"query\":\"test\"}")
+        );
+    }
+
+    #[test]
+    fn dispatch_assistant_uses_block_input_when_no_deltas() {
+        let (_, events) = run_dispatch(serde_json::json!({
+            "type": "assistant",
+            "message": { "content": [
+                { "type": "tool_use", "id": "tu_x", "name": "create_note", "input": { "title": "Hello", "content": "world" } }
+            ] }
+        }));
+        assert!(
+            matches!(&events[0], ClaudeStreamEvent::ToolStart { input: Some(inp), .. }
+                if inp.contains("title") && inp.contains("Hello"))
+        );
+    }
+
+    #[test]
+    fn content_block_stop_clears_current_tool() {
+        let (state, _) = run_dispatch_sequence(vec![
+            serde_json::json!({
+                "type": "stream_event",
+                "event": { "type": "content_block_start", "content_block": { "type": "tool_use", "id": "t1", "name": "x", "input": {} } }
+            }),
+            serde_json::json!({
+                "type": "stream_event",
+                "event": { "type": "content_block_stop" }
+            }),
+        ]);
+        assert!(state.current_tool_id.is_none());
+    }
+
     // --- run_claude_subprocess with mock scripts ---
 
     #[cfg(unix)]

src/components/AiActionCard.test.tsx

@@ -2,61 +2,166 @@ import { describe, it, expect, vi } from 'vitest'
 import { render, screen, fireEvent } from '@testing-library/react'
 import { AiActionCard } from './AiActionCard'
 
+const defaults = {
+  tool: 'create_note',
+  label: 'Creating note... (abc123)',
+  status: 'done' as const,
+  expanded: false,
+  onToggle: vi.fn(),
+}
+
 describe('AiActionCard', () => {
   it('renders label text', () => {
-    render(<AiActionCard tool="create_note" label="Created test.md" status="done" />)
+    render(<AiActionCard {...defaults} label="Created test.md" />)
     expect(screen.getByText('Created test.md')).toBeTruthy()
   })
 
   it('shows pending spinner', () => {
-    render(<AiActionCard tool="search_notes" label="Searching..." status="pending" />)
+    render(<AiActionCard {...defaults} tool="search_notes" label="Searching..." status="pending" />)
     expect(screen.getByTestId('status-pending')).toBeTruthy()
   })
 
   it('shows done check', () => {
-    render(<AiActionCard tool="create_note" label="Created" status="done" />)
+    render(<AiActionCard {...defaults} status="done" />)
     expect(screen.getByTestId('status-done')).toBeTruthy()
   })
 
   it('shows error icon', () => {
-    render(<AiActionCard tool="delete_note" label="Failed" status="error" />)
+    render(<AiActionCard {...defaults} tool="delete_note" label="Failed" status="error" />)
     expect(screen.getByTestId('status-error')).toBeTruthy()
   })
 
-  it('is clickable when path and onOpenNote provided', () => {
+  it('navigates to note when no details and path+onOpenNote provided', () => {
     const onOpenNote = vi.fn()
-    render(<AiActionCard tool="create_note" label="Open note" path="/vault/test.md" status="done" onOpenNote={onOpenNote} />)
-    fireEvent.click(screen.getByTestId('ai-action-card'))
+    const toggle = vi.fn()
+    render(
+      <AiActionCard {...defaults} path="/vault/test.md" onOpenNote={onOpenNote} onToggle={toggle} />,
+    )
+    fireEvent.click(screen.getByTestId('action-card-header'))
     expect(onOpenNote).toHaveBeenCalledWith('/vault/test.md')
+    expect(toggle).not.toHaveBeenCalled()
   })
 
-  it('has button role when clickable', () => {
-    render(<AiActionCard tool="create_note" label="Open note" path="/vault/test.md" status="done" onOpenNote={vi.fn()} />)
-    expect(screen.getByRole('button')).toBeTruthy()
-  })
-
-  it('is not clickable without path', () => {
+  it('toggles expand instead of navigating when details exist', () => {
     const onOpenNote = vi.fn()
-    render(<AiActionCard tool="create_note" label="Created" status="done" onOpenNote={onOpenNote} />)
-    fireEvent.click(screen.getByTestId('ai-action-card'))
+    const toggle = vi.fn()
+    render(
+      <AiActionCard
+        {...defaults}
+        path="/vault/test.md"
+        onOpenNote={onOpenNote}
+        onToggle={toggle}
+        input='{"title":"test"}'
+      />,
+    )
+    fireEvent.click(screen.getByTestId('action-card-header'))
+    expect(toggle).toHaveBeenCalled()
     expect(onOpenNote).not.toHaveBeenCalled()
   })
 
-  it('is not clickable without onOpenNote', () => {
-    render(<AiActionCard tool="create_note" label="Created" path="/vault/test.md" status="done" />)
-    const card = screen.getByTestId('ai-action-card')
-    expect(card.getAttribute('role')).toBeNull()
+  it('header has button role and is focusable', () => {
+    render(<AiActionCard {...defaults} />)
+    const header = screen.getByTestId('action-card-header')
+    expect(header.getAttribute('role')).toBe('button')
+    expect(header.getAttribute('tabindex')).toBe('0')
   })
 
   it('uses lighter background for ui_ tools', () => {
-    render(<AiActionCard tool="ui_open_tab" label="Opened tab" status="done" />)
+    render(<AiActionCard {...defaults} tool="ui_open_tab" label="Opened tab" />)
     const card = screen.getByTestId('ai-action-card')
     expect(card.style.background).toContain('0.06')
   })
 
   it('uses standard background for vault tools', () => {
-    render(<AiActionCard tool="create_note" label="Created" status="done" />)
+    render(<AiActionCard {...defaults} />)
     const card = screen.getByTestId('ai-action-card')
     expect(card.style.background).toContain('0.1')
   })
+
+  // --- Expand / collapse ---
+
+  it('does not show details when collapsed', () => {
+    render(<AiActionCard {...defaults} input='{"q":"test"}' output="found 3" expanded={false} />)
+    expect(screen.queryByTestId('action-card-details')).toBeNull()
+  })
+
+  it('shows details when expanded with input and output', () => {
+    render(<AiActionCard {...defaults} input='{"q":"test"}' output="found 3" expanded />)
+    expect(screen.getByTestId('action-card-details')).toBeTruthy()
+    expect(screen.getByTestId('detail-input')).toBeTruthy()
+    expect(screen.getByTestId('detail-output')).toBeTruthy()
+  })
+
+  it('shows only input when no output', () => {
+    render(<AiActionCard {...defaults} input='{"q":"test"}' expanded />)
+    expect(screen.getByTestId('detail-input')).toBeTruthy()
+    expect(screen.queryByTestId('detail-output')).toBeNull()
+  })
+
+  it('shows only output when no input', () => {
+    render(<AiActionCard {...defaults} output="result text" expanded />)
+    expect(screen.queryByTestId('detail-input')).toBeNull()
+    expect(screen.getByTestId('detail-output')).toBeTruthy()
+  })
+
+  it('does not show details when expanded but no input or output', () => {
+    render(<AiActionCard {...defaults} expanded />)
+    expect(screen.queryByTestId('action-card-details')).toBeNull()
+  })
+
+  it('formats JSON input prettily', () => {
+    render(<AiActionCard {...defaults} input='{"title":"Hello","content":"world"}' expanded />)
+    const inputBlock = screen.getByTestId('detail-input')
+    expect(inputBlock.textContent).toContain('"title": "Hello"')
+  })
+
+  it('truncates very long output', () => {
+    const longOutput = 'x'.repeat(1000)
+    render(<AiActionCard {...defaults} output={longOutput} expanded />)
+    const outputBlock = screen.getByTestId('detail-output')
+    expect(outputBlock.textContent!.length).toBeLessThan(1000)
+  })
+
+  // --- Keyboard accessibility ---
+
+  it('expands on Enter key', () => {
+    const toggle = vi.fn()
+    render(<AiActionCard {...defaults} onToggle={toggle} input='{"a":1}' />)
+    fireEvent.keyDown(screen.getByTestId('action-card-header'), { key: 'Enter' })
+    expect(toggle).toHaveBeenCalled()
+  })
+
+  it('expands on Space key', () => {
+    const toggle = vi.fn()
+    render(<AiActionCard {...defaults} onToggle={toggle} input='{"a":1}' />)
+    fireEvent.keyDown(screen.getByTestId('action-card-header'), { key: ' ' })
+    expect(toggle).toHaveBeenCalled()
+  })
+
+  it('collapses on Escape key when expanded', () => {
+    const toggle = vi.fn()
+    render(<AiActionCard {...defaults} onToggle={toggle} expanded input='{"a":1}' />)
+    fireEvent.keyDown(screen.getByTestId('action-card-header'), { key: 'Escape' })
+    expect(toggle).toHaveBeenCalled()
+  })
+
+  it('does not collapse on Escape when already collapsed', () => {
+    const toggle = vi.fn()
+    render(<AiActionCard {...defaults} onToggle={toggle} expanded={false} input='{"a":1}' />)
+    fireEvent.keyDown(screen.getByTestId('action-card-header'), { key: 'Escape' })
+    expect(toggle).not.toHaveBeenCalled()
+  })
+
+  it('sets aria-expanded attribute', () => {
+    const { rerender } = render(<AiActionCard {...defaults} expanded={false} />)
+    expect(screen.getByTestId('action-card-header').getAttribute('aria-expanded')).toBe('false')
+    rerender(<AiActionCard {...defaults} expanded />)
+    expect(screen.getByTestId('action-card-header').getAttribute('aria-expanded')).toBe('true')
+  })
+
+  it('shows error output in red for error status', () => {
+    render(<AiActionCard {...defaults} status="error" output="Permission denied" expanded />)
+    const outputBlock = screen.getByTestId('detail-output')
+    expect(outputBlock.style.color).toContain('destructive')
+  })
 })

src/components/AiActionCard.tsx

@@ -1,7 +1,7 @@
-import type { ReactNode } from 'react'
+import { type KeyboardEvent, type ReactNode, useCallback } from 'react'
 import {
   PencilSimple, MagnifyingGlass, Link, Trash, ChartBar, Eye, Sparkle,
-  CircleNotch, CheckCircle, XCircle,
+  CircleNotch, CheckCircle, XCircle, CaretRight, CaretDown,
 } from '@phosphor-icons/react'
 
 export type AiActionStatus = 'pending' | 'done' | 'error'
@@ -11,9 +11,15 @@ export interface AiActionCardProps {
   label: string
   path?: string
   status: AiActionStatus
+  input?: string
+  output?: string
+  expanded: boolean
+  onToggle: () => void
   onOpenNote?: (path: string) => void
 }
 
+const MAX_DETAIL_LENGTH = 800
+
 type IconRenderer = (size: number) => ReactNode
 
 const TOOL_ICON_MAP: Record<string, IconRenderer> = {
@@ -43,27 +49,118 @@ function StatusIndicator({ status }: { status: AiActionStatus }) {
   return <XCircle size={14} weight="fill" style={{ color: 'var(--destructive)' }} data-testid="status-error" />
 }
 
-export function AiActionCard({ tool, label, path, status, onOpenNote }: AiActionCardProps) {
-  const renderIcon = TOOL_ICON_MAP[tool] ?? DEFAULT_ICON
-  const isClickable = !!path && !!onOpenNote
-  const isUiTool = tool.startsWith('ui_')
+function truncateText(text: string): { text: string; truncated: boolean } {
+  if (text.length <= MAX_DETAIL_LENGTH) return { text, truncated: false }
+  return { text: text.slice(0, MAX_DETAIL_LENGTH), truncated: true }
+}
 
+function formatInputForDisplay(raw: string): string {
+  try {
+    return JSON.stringify(JSON.parse(raw), null, 2)
+  } catch {
+    return raw
+  }
+}
+
+function DetailBlock({ label, content, isError }: {
+  label: string; content: string; isError?: boolean
+}) {
+  const { text, truncated } = truncateText(content)
   return (
-    <div
-      className="flex items-center gap-2 rounded"
-      style={{
-        padding: '6px 10px',
-        fontSize: 12,
-        background: isUiTool ? 'rgba(74, 158, 255, 0.06)' : 'rgba(74, 158, 255, 0.1)',
-        cursor: isClickable ? 'pointer' : 'default',
-      }}
-      onClick={isClickable ? () => onOpenNote(path) : undefined}
-      role={isClickable ? 'button' : undefined}
-      data-testid="ai-action-card"
-    >
-      <span className="shrink-0 text-muted-foreground">{renderIcon(14)}</span>
-      <span className="flex-1 truncate">{label}</span>
-      <StatusIndicator status={status} />
+    <div style={{ marginTop: 6 }}>
+      <div
+        className="text-muted-foreground"
+        style={{ fontSize: 10, fontWeight: 600, textTransform: 'uppercase', marginBottom: 2 }}
+      >
+        {label}
+      </div>
+      <pre
+        data-testid={`detail-${label.toLowerCase()}`}
+        style={{
+          fontSize: 11,
+          lineHeight: 1.4,
+          margin: 0,
+          padding: '4px 6px',
+          borderRadius: 4,
+          background: 'var(--muted)',
+          color: isError ? 'var(--destructive)' : 'var(--foreground)',
+          whiteSpace: 'pre-wrap',
+          wordBreak: 'break-word',
+          maxHeight: 200,
+          overflow: 'auto',
+        }}
+      >
+        {text}{truncated && <span className="text-muted-foreground">{'…'}</span>}
+      </pre>
+    </div>
+  )
+}
+
+export function AiActionCard({
+  tool, label, path, status, input, output, expanded, onToggle, onOpenNote,
+}: AiActionCardProps) {
+  const renderIcon = TOOL_ICON_MAP[tool] ?? DEFAULT_ICON
+  const isUiTool = tool.startsWith('ui_')
+  const hasDetails = !!(input || output)
+
+  const handleKeyDown = useCallback((e: KeyboardEvent) => {
+    if (e.key === 'Enter' || e.key === ' ') {
+      e.preventDefault()
+      onToggle()
+    } else if (e.key === 'Escape' && expanded) {
+      e.preventDefault()
+      onToggle()
+    }
+  }, [onToggle, expanded])
+
+  const handleClick = useCallback(() => {
+    if (path && onOpenNote && !hasDetails) {
+      onOpenNote(path)
+    } else {
+      onToggle()
+    }
+  }, [path, onOpenNote, hasDetails, onToggle])
+
+  const formattedInput = input ? formatInputForDisplay(input) : undefined
+
+  return (
+    <div
+      data-testid="ai-action-card"
+      className="rounded"
+      style={{
+        fontSize: 12,
+        background: isUiTool ? 'rgba(74, 158, 255, 0.06)' : 'rgba(74, 158, 255, 0.1)',
+      }}
+    >
+      <div
+        className="flex items-center gap-2"
+        style={{ padding: '6px 10px', cursor: 'pointer' }}
+        role="button"
+        tabIndex={0}
+        aria-expanded={expanded}
+        onClick={handleClick}
+        onKeyDown={handleKeyDown}
+        data-testid="action-card-header"
+      >
+        <span className="shrink-0 text-muted-foreground" style={{ width: 14, display: 'flex' }}>
+          {hasDetails
+            ? (expanded ? <CaretDown size={12} /> : <CaretRight size={12} />)
+            : renderIcon(14)}
+        </span>
+        <span className="flex-1 truncate">{label}</span>
+        <StatusIndicator status={status} />
+      </div>
+      {expanded && hasDetails && (
+        <div
+          data-testid="action-card-details"
+          style={{ padding: '0 10px 8px 10px' }}
+        >
+          {formattedInput && <DetailBlock label="Input" content={formattedInput} />}
+          {output && (
+            <DetailBlock label="Output" content={output} isError={status === 'error'} />
+          )}
+        </div>
+      )}
     </div>
   )
 }

src/components/AiMessage.test.tsx

@@ -44,8 +44,8 @@ describe('AiMessage', () => {
       <AiMessage
         userMessage="Do something"
         actions={[
-          { tool: 'create_note', label: 'Created test.md', status: 'done' },
-          { tool: 'search_notes', label: 'Searched', status: 'pending' },
+          { tool: 'create_note', toolId: 't1', label: 'Created test.md', status: 'done' },
+          { tool: 'search_notes', toolId: 't2', label: 'Searched', status: 'pending' },
         ]}
       />,
     )
@@ -57,11 +57,11 @@ describe('AiMessage', () => {
     render(
       <AiMessage
         userMessage="Do"
-        actions={[{ tool: 'create_note', label: 'Open', path: '/vault/note.md', status: 'done' }]}
+        actions={[{ tool: 'create_note', toolId: 't1', label: 'Open', path: '/vault/note.md', status: 'done' }]}
         onOpenNote={onOpenNote}
       />,
     )
-    fireEvent.click(screen.getByTestId('ai-action-card'))
+    fireEvent.click(screen.getByTestId('action-card-header'))
     expect(onOpenNote).toHaveBeenCalledWith('/vault/note.md')
   })
 
@@ -88,4 +88,28 @@ describe('AiMessage', () => {
     render(<AiMessage userMessage="Ask" actions={[]} />)
     expect(screen.queryByTestId('ai-action-card')).toBeNull()
   })
+
+  it('expands and collapses action cards independently', () => {
+    render(
+      <AiMessage
+        userMessage="Do"
+        actions={[
+          { tool: 'search_notes', toolId: 't1', label: 'Searched', status: 'done', input: '{"q":"test"}', output: 'Found 3' },
+          { tool: 'create_note', toolId: 't2', label: 'Created', status: 'done', input: '{"title":"x"}' },
+        ]}
+      />,
+    )
+    const headers = screen.getAllByTestId('action-card-header')
+    // Both collapsed initially
+    expect(screen.queryByTestId('action-card-details')).toBeNull()
+    // Expand first card
+    fireEvent.click(headers[0])
+    expect(screen.getAllByTestId('action-card-details')).toHaveLength(1)
+    // Expand second card too
+    fireEvent.click(headers[1])
+    expect(screen.getAllByTestId('action-card-details')).toHaveLength(2)
+    // Collapse first card
+    fireEvent.click(headers[0])
+    expect(screen.getAllByTestId('action-card-details')).toHaveLength(1)
+  })
 })

src/components/AiMessage.tsx

@@ -1,12 +1,15 @@
-import { useState } from 'react'
+import { useState, useCallback } from 'react'
 import { CaretRight, CaretDown, Brain, ArrowCounterClockwise } from '@phosphor-icons/react'
 import { AiActionCard, type AiActionStatus } from './AiActionCard'
 
 export interface AiAction {
   tool: string
+  toolId: string
   label: string
   path?: string
   status: AiActionStatus
+  input?: string
+  output?: string
 }
 
 export interface AiMessageProps {
@@ -66,18 +69,25 @@ function ReasoningBlock({ text, expanded, onToggle }: {
   )
 }
 
-function ActionCardsList({ actions, onOpenNote }: {
-  actions: AiAction[]; onOpenNote?: (path: string) => void
+function ActionCardsList({ actions, onOpenNote, expandedIds, onToggleExpand }: {
+  actions: AiAction[]
+  onOpenNote?: (path: string) => void
+  expandedIds: Set<string>
+  onToggleExpand: (toolId: string) => void
 }) {
   return (
     <div className="flex flex-col gap-1" style={{ marginBottom: 8 }}>
-      {actions.map((action, i) => (
+      {actions.map((action) => (
         <AiActionCard
-          key={`${action.tool}-${i}`}
+          key={action.toolId}
           tool={action.tool}
           label={action.label}
           path={action.path}
           status={action.status}
+          input={action.input}
+          output={action.output}
+          expanded={expandedIds.has(action.toolId)}
+          onToggle={() => onToggleExpand(action.toolId)}
           onOpenNote={onOpenNote}
         />
       ))}
@@ -115,6 +125,16 @@ function StreamingIndicator() {
 
 export function AiMessage({ userMessage, reasoning, actions, response, isStreaming, onOpenNote }: AiMessageProps) {
   const [reasoningExpanded, setReasoningExpanded] = useState(false)
+  const [expandedActions, setExpandedActions] = useState<Set<string>>(new Set())
+
+  const toggleAction = useCallback((toolId: string) => {
+    setExpandedActions(prev => {
+      const next = new Set(prev)
+      if (next.has(toolId)) next.delete(toolId)
+      else next.add(toolId)
+      return next
+    })
+  }, [])
 
   return (
     <div data-testid="ai-message" style={{ marginBottom: 16 }}>
@@ -126,7 +146,14 @@ export function AiMessage({ userMessage, reasoning, actions, response, isStreami
           onToggle={() => setReasoningExpanded(!reasoningExpanded)}
         />
       )}
-      {actions.length > 0 && <ActionCardsList actions={actions} onOpenNote={onOpenNote} />}
+      {actions.length > 0 && (
+        <ActionCardsList
+          actions={actions}
+          onOpenNote={onOpenNote}
+          expandedIds={expandedActions}
+          onToggleExpand={toggleAction}
+        />
+      )}
       {response && <ResponseBlock text={response} />}
       {isStreaming && !response && <StreamingIndicator />}
     </div>

src/hooks/useAiAgent.ts

@@ -63,23 +63,54 @@ export function useAiAgent(vaultPath: string, contextPrompt?: string) {
         update(m => ({ ...m, response: (m.response ?? '') + text }))
       },
 
-      onToolStart: (toolName, toolId) => {
+      onToolStart: (toolName, toolId, input) => {
         if (abortRef.current.aborted) return
         setStatus('tool-executing')
+        update(m => {
+          const existing = m.actions.find(a => a.toolId === toolId)
+          if (existing) {
+            // Re-emitted with input data — update the existing action
+            return {
+              ...m,
+              actions: m.actions.map(a =>
+                a.toolId === toolId ? { ...a, input: input ?? a.input } : a,
+              ),
+            }
+          }
+          return {
+            ...m,
+            actions: [...m.actions, {
+              tool: toolName,
+              toolId,
+              label: formatToolLabel(toolName, toolId),
+              status: 'pending' as const,
+              input,
+            }],
+          }
+        })
+      },
+
+      onToolDone: (toolId, output) => {
+        if (abortRef.current.aborted) return
         update(m => ({
           ...m,
-          actions: [...m.actions, {
-            tool: toolName,
-            label: formatToolLabel(toolName, toolId),
-            status: 'pending' as const,
-          }],
+          actions: m.actions.map(a =>
+            a.toolId === toolId ? { ...a, status: 'done' as const, output } : a,
+          ),
         }))
       },
 
       onError: (error) => {
         if (abortRef.current.aborted) return
         setStatus('error')
-        update(m => ({ ...m, isStreaming: false, response: (m.response ?? '') + `\nError: ${error}` }))
+        update(m => ({
+          ...m,
+          isStreaming: false,
+          response: (m.response ?? '') + `\nError: ${error}`,
+          actions: m.actions.map(a =>
+            a.status === 'pending' ? { ...a, status: 'error' as const } : a,
+          ),
+        }))
       },
 
       onDone: () => {

src/utils/ai-agent.ts

@@ -24,15 +24,16 @@ export function buildAgentSystemPrompt(vaultContext?: string): string {
 type ClaudeAgentStreamEvent =
   | { kind: 'Init'; session_id: string }
   | { kind: 'TextDelta'; text: string }
-  | { kind: 'ToolStart'; tool_name: string; tool_id: string }
-  | { kind: 'ToolDone'; tool_id: string }
+  | { kind: 'ToolStart'; tool_name: string; tool_id: string; input?: string }
+  | { kind: 'ToolDone'; tool_id: string; output?: string }
   | { kind: 'Result'; text: string; session_id: string }
   | { kind: 'Error'; message: string }
   | { kind: 'Done' }
 
 export interface AgentStreamCallbacks {
   onText: (text: string) => void
-  onToolStart: (toolName: string, toolId: string) => void
+  onToolStart: (toolName: string, toolId: string, input?: string) => void
+  onToolDone: (toolId: string, output?: string) => void
   onError: (message: string) => void
   onDone: () => void
 }
@@ -65,7 +66,10 @@ export async function streamClaudeAgent(
         callbacks.onText(data.text)
         break
       case 'ToolStart':
-        callbacks.onToolStart(data.tool_name, data.tool_id)
+        callbacks.onToolStart(data.tool_name, data.tool_id, data.input)
+        break
+      case 'ToolDone':
+        callbacks.onToolDone(data.tool_id, data.output)
         break
       case 'Error':
         callbacks.onError(data.message)