Expose structured thinking without polluting normal assistant output

Extended thinking needed to travel end-to-end through the API,
runtime, and CLI so the client can request a thinking budget,
preserve streamed reasoning blocks, and present them in a
collapsed text-first form. The implementation keeps thinking
strictly opt-in, adds a session-local toggle, and reuses the
existing flag/slash-command/reporting surfaces instead of
introducing a new UI layer.

Constraint: Existing non-thinking text/tool flows had to remain backward compatible by default
Constraint: Terminal UX needed a lightweight collapsed representation rather than an interactive TUI widget
Rejected: Heuristic CLI-only parsing of reasoning text | brittle against structured stream payloads
Rejected: Expanded raw thinking output by default | too noisy for normal assistant responses
Confidence: medium
Scope-risk: moderate
Reversibility: clean
Directive: Keep thinking blocks structurally separate from answer text unless the upstream API contract changes
Tested: cargo fmt --all; cargo clippy --workspace --all-targets -- -D warnings; cargo test -q
Not-tested: Live upstream thinking payloads against the production API contract

rust/README.md

@@ -102,6 +102,13 @@ cd rust
 cargo run -p rusty-claude-cli -- --model claude-sonnet-4-20250514 prompt "List the key crates in this workspace"
 ```
 
+Restrict enabled tools in an interactive session:
+
+```bash
+cd rust
+cargo run -p rusty-claude-cli -- --allowedTools read,glob
+```
+
 ### 2) REPL mode
 
 Start the interactive shell:
@@ -123,6 +130,10 @@ Inside the REPL, useful commands include:
 /memory
 /config
 /init
+/diff
+/version
+/export notes.txt
+/session list
 /exit
 ```
 
@@ -169,6 +180,10 @@ cargo run -p rusty-claude-cli -- --resume session.json /memory /config
 - `/config [env|hooks|model]` — inspect discovered Claude config
 - `/memory` — inspect loaded instruction memory files
 - `/init` — create a starter `CLAUDE.md`
+- `/diff` — show the current git diff for the workspace
+- `/version` — print version and build metadata locally
+- `/export [file]` — export the current conversation transcript
+- `/session [list|switch <session-id>]` — inspect or switch managed local sessions
 - `/exit` — leave the REPL
 
 ## Environment variables

rust/crates/api/src/client.rs

@@ -392,8 +392,52 @@ pub fn resolve_saved_oauth_token(config: &OAuthConfig) -> Result<Option<OAuthTok
     let Some(token_set) = load_saved_oauth_token()? else {
         return Ok(None);
     };
+    resolve_saved_oauth_token_set(config, token_set).map(Some)
+}
+
+pub fn resolve_startup_auth_source<F>(load_oauth_config: F) -> Result<AuthSource, ApiError>
+where
+    F: FnOnce() -> Result<Option<OAuthConfig>, ApiError>,
+{
+    if let Some(api_key) = read_env_non_empty("ANTHROPIC_API_KEY")? {
+        return match read_env_non_empty("ANTHROPIC_AUTH_TOKEN")? {
+            Some(bearer_token) => Ok(AuthSource::ApiKeyAndBearer {
+                api_key,
+                bearer_token,
+            }),
+            None => Ok(AuthSource::ApiKey(api_key)),
+        };
+    }
+    if let Some(bearer_token) = read_env_non_empty("ANTHROPIC_AUTH_TOKEN")? {
+        return Ok(AuthSource::BearerToken(bearer_token));
+    }
+
+    let Some(token_set) = load_saved_oauth_token()? else {
+        return Err(ApiError::MissingApiKey);
+    };
     if !oauth_token_is_expired(&token_set) {
-        return Ok(Some(token_set));
+        return Ok(AuthSource::BearerToken(token_set.access_token));
+    }
+    if token_set.refresh_token.is_none() {
+        return Err(ApiError::ExpiredOAuthToken);
+    }
+
+    let Some(config) = load_oauth_config()? else {
+        return Err(ApiError::Auth(
+            "saved OAuth token is expired; runtime OAuth config is missing".to_string(),
+        ));
+    };
+    Ok(AuthSource::from(resolve_saved_oauth_token_set(
+        &config, token_set,
+    )?))
+}
+
+fn resolve_saved_oauth_token_set(
+    config: &OAuthConfig,
+    token_set: OAuthTokenSet,
+) -> Result<OAuthTokenSet, ApiError> {
+    if !oauth_token_is_expired(&token_set) {
+        return Ok(token_set);
     }
     let Some(refresh_token) = token_set.refresh_token.clone() else {
         return Err(ApiError::ExpiredOAuthToken);
@@ -403,18 +447,28 @@ pub fn resolve_saved_oauth_token(config: &OAuthConfig) -> Result<Option<OAuthTok
         client
             .refresh_oauth_token(
                 config,
-                &OAuthRefreshRequest::from_config(config, refresh_token, Some(token_set.scopes)),
+                &OAuthRefreshRequest::from_config(
+                    config,
+                    refresh_token,
+                    Some(token_set.scopes.clone()),
+                ),
             )
             .await
     })?;
-    save_oauth_credentials(&runtime::OAuthTokenSet {
-        access_token: refreshed.access_token.clone(),
-        refresh_token: refreshed.refresh_token.clone(),
+    let resolved = OAuthTokenSet {
+        access_token: refreshed.access_token,
+        refresh_token: refreshed.refresh_token.or(token_set.refresh_token),
         expires_at: refreshed.expires_at,
-        scopes: refreshed.scopes.clone(),
+        scopes: refreshed.scopes,
+    };
+    save_oauth_credentials(&runtime::OAuthTokenSet {
+        access_token: resolved.access_token.clone(),
+        refresh_token: resolved.refresh_token.clone(),
+        expires_at: resolved.expires_at,
+        scopes: resolved.scopes.clone(),
     })
     .map_err(ApiError::from)?;
-    Ok(Some(refreshed))
+    Ok(resolved)
 }
 
 fn client_runtime_block_on<F, T>(future: F) -> Result<T, ApiError>
@@ -571,8 +625,8 @@ mod tests {
     use runtime::{clear_oauth_credentials, save_oauth_credentials, OAuthConfig};
 
     use crate::client::{
-        now_unix_timestamp, oauth_token_is_expired, resolve_saved_oauth_token, AnthropicClient,
-        AuthSource, OAuthTokenSet,
+        now_unix_timestamp, oauth_token_is_expired, resolve_saved_oauth_token,
+        resolve_startup_auth_source, AnthropicClient, AuthSource, OAuthTokenSet,
     };
     use crate::types::{ContentBlockDelta, MessageRequest};
 
@@ -760,6 +814,95 @@ mod tests {
         std::fs::remove_dir_all(config_home).expect("cleanup temp dir");
     }
 
+    #[test]
+    fn resolve_startup_auth_source_uses_saved_oauth_without_loading_config() {
+        let _guard = env_lock();
+        let config_home = temp_config_home();
+        std::env::set_var("CLAUDE_CONFIG_HOME", &config_home);
+        std::env::remove_var("ANTHROPIC_AUTH_TOKEN");
+        std::env::remove_var("ANTHROPIC_API_KEY");
+        save_oauth_credentials(&runtime::OAuthTokenSet {
+            access_token: "saved-access-token".to_string(),
+            refresh_token: Some("refresh".to_string()),
+            expires_at: Some(now_unix_timestamp() + 300),
+            scopes: vec!["scope:a".to_string()],
+        })
+        .expect("save oauth credentials");
+
+        let auth = resolve_startup_auth_source(|| panic!("config should not be loaded"))
+            .expect("startup auth");
+        assert_eq!(auth.bearer_token(), Some("saved-access-token"));
+
+        clear_oauth_credentials().expect("clear credentials");
+        std::env::remove_var("CLAUDE_CONFIG_HOME");
+        std::fs::remove_dir_all(config_home).expect("cleanup temp dir");
+    }
+
+    #[test]
+    fn resolve_startup_auth_source_errors_when_refreshable_token_lacks_config() {
+        let _guard = env_lock();
+        let config_home = temp_config_home();
+        std::env::set_var("CLAUDE_CONFIG_HOME", &config_home);
+        std::env::remove_var("ANTHROPIC_AUTH_TOKEN");
+        std::env::remove_var("ANTHROPIC_API_KEY");
+        save_oauth_credentials(&runtime::OAuthTokenSet {
+            access_token: "expired-access-token".to_string(),
+            refresh_token: Some("refresh-token".to_string()),
+            expires_at: Some(1),
+            scopes: vec!["scope:a".to_string()],
+        })
+        .expect("save expired oauth credentials");
+
+        let error =
+            resolve_startup_auth_source(|| Ok(None)).expect_err("missing config should error");
+        assert!(
+            matches!(error, crate::error::ApiError::Auth(message) if message.contains("runtime OAuth config is missing"))
+        );
+
+        let stored = runtime::load_oauth_credentials()
+            .expect("load stored credentials")
+            .expect("stored token set");
+        assert_eq!(stored.access_token, "expired-access-token");
+        assert_eq!(stored.refresh_token.as_deref(), Some("refresh-token"));
+
+        clear_oauth_credentials().expect("clear credentials");
+        std::env::remove_var("CLAUDE_CONFIG_HOME");
+        std::fs::remove_dir_all(config_home).expect("cleanup temp dir");
+    }
+
+    #[test]
+    fn resolve_saved_oauth_token_preserves_refresh_token_when_refresh_response_omits_it() {
+        let _guard = env_lock();
+        let config_home = temp_config_home();
+        std::env::set_var("CLAUDE_CONFIG_HOME", &config_home);
+        std::env::remove_var("ANTHROPIC_AUTH_TOKEN");
+        std::env::remove_var("ANTHROPIC_API_KEY");
+        save_oauth_credentials(&runtime::OAuthTokenSet {
+            access_token: "expired-access-token".to_string(),
+            refresh_token: Some("refresh-token".to_string()),
+            expires_at: Some(1),
+            scopes: vec!["scope:a".to_string()],
+        })
+        .expect("save expired oauth credentials");
+
+        let token_url = spawn_token_server(
+            "{\"access_token\":\"refreshed-token\",\"expires_at\":9999999999,\"scopes\":[\"scope:a\"]}",
+        );
+        let resolved = resolve_saved_oauth_token(&sample_oauth_config(token_url))
+            .expect("resolve refreshed token")
+            .expect("token set present");
+        assert_eq!(resolved.access_token, "refreshed-token");
+        assert_eq!(resolved.refresh_token.as_deref(), Some("refresh-token"));
+        let stored = runtime::load_oauth_credentials()
+            .expect("load stored credentials")
+            .expect("stored token set");
+        assert_eq!(stored.refresh_token.as_deref(), Some("refresh-token"));
+
+        clear_oauth_credentials().expect("clear credentials");
+        std::env::remove_var("CLAUDE_CONFIG_HOME");
+        std::fs::remove_dir_all(config_home).expect("cleanup temp dir");
+    }
+
     #[test]
     fn message_request_stream_helper_sets_stream_true() {
         let request = MessageRequest {
@@ -769,6 +912,7 @@ mod tests {
             system: None,
             tools: None,
             tool_choice: None,
+            thinking: None,
             stream: false,
         };
 

rust/crates/api/src/lib.rs

@@ -4,8 +4,8 @@ mod sse;
 mod types;
 
 pub use client::{
-    oauth_token_is_expired, resolve_saved_oauth_token, AnthropicClient, AuthSource, MessageStream,
-    OAuthTokenSet,
+    oauth_token_is_expired, resolve_saved_oauth_token, resolve_startup_auth_source,
+    AnthropicClient, AuthSource, MessageStream, OAuthTokenSet,
 };
 pub use error::ApiError;
 pub use sse::{parse_frame, SseParser};
@@ -13,5 +13,5 @@ pub use types::{
     ContentBlockDelta, ContentBlockDeltaEvent, ContentBlockStartEvent, ContentBlockStopEvent,
     InputContentBlock, InputMessage, MessageDelta, MessageDeltaEvent, MessageRequest,
     MessageResponse, MessageStartEvent, MessageStopEvent, OutputContentBlock, StreamEvent,
-    ToolChoice, ToolDefinition, ToolResultContentBlock, Usage,
+    ThinkingConfig, ToolChoice, ToolDefinition, ToolResultContentBlock, Usage,
 };

rust/crates/api/src/types.rs

@@ -12,6 +12,8 @@ pub struct MessageRequest {
     pub tools: Option<Vec<ToolDefinition>>,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub tool_choice: Option<ToolChoice>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub thinking: Option<ThinkingConfig>,
     #[serde(default, skip_serializing_if = "std::ops::Not::not")]
     pub stream: bool,
 }
@@ -24,6 +26,23 @@ impl MessageRequest {
     }
 }
 
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+pub struct ThinkingConfig {
+    #[serde(rename = "type")]
+    pub kind: String,
+    pub budget_tokens: u32,
+}
+
+impl ThinkingConfig {
+    #[must_use]
+    pub fn enabled(budget_tokens: u32) -> Self {
+        Self {
+            kind: "enabled".to_string(),
+            budget_tokens,
+        }
+    }
+}
+
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 pub struct InputMessage {
     pub role: String,
@@ -130,6 +149,11 @@ pub enum OutputContentBlock {
     Text {
         text: String,
     },
+    Thinking {
+        thinking: String,
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        signature: Option<String>,
+    },
     ToolUse {
         id: String,
         name: String,
@@ -189,6 +213,8 @@ pub struct ContentBlockDeltaEvent {
 #[serde(tag = "type", rename_all = "snake_case")]
 pub enum ContentBlockDelta {
     TextDelta { text: String },
+    ThinkingDelta { thinking: String },
+    SignatureDelta { signature: String },
     InputJsonDelta { partial_json: String },
 }
 

rust/crates/api/tests/client_integration.rs

@@ -258,6 +258,7 @@ async fn live_stream_smoke_test() {
             system: None,
             tools: None,
             tool_choice: None,
+            thinking: None,
             stream: false,
         })
         .await
@@ -438,6 +439,7 @@ fn sample_request(stream: bool) -> MessageRequest {
             }),
         }]),
         tool_choice: Some(ToolChoice::Auto),
+        thinking: None,
         stream,
     }
 }

rust/crates/commands/src/lib.rs

@@ -57,6 +57,12 @@ const SLASH_COMMAND_SPECS: &[SlashCommandSpec] = &[
         argument_hint: None,
         resume_supported: true,
     },
+    SlashCommandSpec {
+        name: "thinking",
+        summary: "Show or toggle extended thinking",
+        argument_hint: Some("[on|off]"),
+        resume_supported: false,
+    },
     SlashCommandSpec {
         name: "model",
         summary: "Show or switch the active model",
@@ -136,6 +142,9 @@ pub enum SlashCommand {
     Help,
     Status,
     Compact,
+    Thinking {
+        enabled: Option<bool>,
+    },
     Model {
         model: Option<String>,
     },
@@ -180,6 +189,13 @@ impl SlashCommand {
             "help" => Self::Help,
             "status" => Self::Status,
             "compact" => Self::Compact,
+            "thinking" => Self::Thinking {
+                enabled: match parts.next() {
+                    Some("on") => Some(true),
+                    Some("off") => Some(false),
+                    Some(_) | None => None,
+                },
+            },
             "model" => Self::Model {
                 model: parts.next().map(ToOwned::to_owned),
             },
@@ -279,6 +295,7 @@ pub fn handle_slash_command(
             session: session.clone(),
         }),
         SlashCommand::Status
+        | SlashCommand::Thinking { .. }
         | SlashCommand::Model { .. }
         | SlashCommand::Permissions { .. }
         | SlashCommand::Clear { .. }
@@ -307,6 +324,22 @@ mod tests {
     fn parses_supported_slash_commands() {
         assert_eq!(SlashCommand::parse("/help"), Some(SlashCommand::Help));
         assert_eq!(SlashCommand::parse(" /status "), Some(SlashCommand::Status));
+        assert_eq!(
+            SlashCommand::parse("/thinking on"),
+            Some(SlashCommand::Thinking {
+                enabled: Some(true),
+            })
+        );
+        assert_eq!(
+            SlashCommand::parse("/thinking off"),
+            Some(SlashCommand::Thinking {
+                enabled: Some(false),
+            })
+        );
+        assert_eq!(
+            SlashCommand::parse("/thinking"),
+            Some(SlashCommand::Thinking { enabled: None })
+        );
         assert_eq!(
             SlashCommand::parse("/model claude-opus"),
             Some(SlashCommand::Model {
@@ -374,6 +407,7 @@ mod tests {
         assert!(help.contains("/help"));
         assert!(help.contains("/status"));
         assert!(help.contains("/compact"));
+        assert!(help.contains("/thinking [on|off]"));
         assert!(help.contains("/model [model]"));
         assert!(help.contains("/permissions [read-only|workspace-write|danger-full-access]"));
         assert!(help.contains("/clear [--confirm]"));
@@ -386,7 +420,7 @@ mod tests {
         assert!(help.contains("/version"));
         assert!(help.contains("/export [file]"));
         assert!(help.contains("/session [list|switch <session-id>]"));
-        assert_eq!(slash_command_specs().len(), 15);
+        assert_eq!(slash_command_specs().len(), 16);
         assert_eq!(resume_supported_slash_commands().len(), 11);
     }
 
@@ -434,6 +468,9 @@ mod tests {
         let session = Session::new();
         assert!(handle_slash_command("/unknown", &session, CompactionConfig::default()).is_none());
         assert!(handle_slash_command("/status", &session, CompactionConfig::default()).is_none());
+        assert!(
+            handle_slash_command("/thinking on", &session, CompactionConfig::default()).is_none()
+        );
         assert!(
             handle_slash_command("/model claude", &session, CompactionConfig::default()).is_none()
         );

rust/crates/runtime/src/compact.rs

@@ -130,7 +130,7 @@ fn summarize_messages(messages: &[ConversationMessage]) -> String {
         .filter_map(|block| match block {
             ContentBlock::ToolUse { name, .. } => Some(name.as_str()),
             ContentBlock::ToolResult { tool_name, .. } => Some(tool_name.as_str()),
-            ContentBlock::Text { .. } => None,
+            ContentBlock::Text { .. } | ContentBlock::Thinking { .. } => None,
         })
         .collect::<Vec<_>>();
     tool_names.sort_unstable();
@@ -200,6 +200,7 @@ fn summarize_messages(messages: &[ConversationMessage]) -> String {
 fn summarize_block(block: &ContentBlock) -> String {
     let raw = match block {
         ContentBlock::Text { text } => text.clone(),
+        ContentBlock::Thinking { text, .. } => format!("thinking: {text}"),
         ContentBlock::ToolUse { name, input, .. } => format!("tool_use {name}({input})"),
         ContentBlock::ToolResult {
             tool_name,
@@ -258,7 +259,7 @@ fn collect_key_files(messages: &[ConversationMessage]) -> Vec<String> {
         .iter()
         .flat_map(|message| message.blocks.iter())
         .map(|block| match block {
-            ContentBlock::Text { text } => text.as_str(),
+            ContentBlock::Text { text } | ContentBlock::Thinking { text, .. } => text.as_str(),
             ContentBlock::ToolUse { input, .. } => input.as_str(),
             ContentBlock::ToolResult { output, .. } => output.as_str(),
         })
@@ -280,10 +281,15 @@ fn infer_current_work(messages: &[ConversationMessage]) -> Option<String> {
 
 fn first_text_block(message: &ConversationMessage) -> Option<&str> {
     message.blocks.iter().find_map(|block| match block {
-        ContentBlock::Text { text } if !text.trim().is_empty() => Some(text.as_str()),
+        ContentBlock::Text { text } | ContentBlock::Thinking { text, .. }
+            if !text.trim().is_empty() =>
+        {
+            Some(text.as_str())
+        }
         ContentBlock::ToolUse { .. }
         | ContentBlock::ToolResult { .. }
-        | ContentBlock::Text { .. } => None,
+        | ContentBlock::Text { .. }
+        | ContentBlock::Thinking { .. } => None,
     })
 }
 
@@ -328,7 +334,7 @@ fn estimate_message_tokens(message: &ConversationMessage) -> usize {
         .blocks
         .iter()
         .map(|block| match block {
-            ContentBlock::Text { text } => text.len() / 4 + 1,
+            ContentBlock::Text { text } | ContentBlock::Thinking { text, .. } => text.len() / 4 + 1,
             ContentBlock::ToolUse { name, input, .. } => (name.len() + input.len()) / 4 + 1,
             ContentBlock::ToolResult {
                 tool_name, output, ..

rust/crates/runtime/src/conversation.rs

@@ -17,6 +17,8 @@ pub struct ApiRequest {
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum AssistantEvent {
     TextDelta(String),
+    ThinkingDelta(String),
+    ThinkingSignature(String),
     ToolUse {
         id: String,
         name: String,
@@ -247,15 +249,26 @@ fn build_assistant_message(
     events: Vec<AssistantEvent>,
 ) -> Result<(ConversationMessage, Option<TokenUsage>), RuntimeError> {
     let mut text = String::new();
+    let mut thinking = String::new();
+    let mut thinking_signature: Option<String> = None;
     let mut blocks = Vec::new();
     let mut finished = false;
     let mut usage = None;
 
     for event in events {
         match event {
-            AssistantEvent::TextDelta(delta) => text.push_str(&delta),
+            AssistantEvent::TextDelta(delta) => {
+                flush_thinking_block(&mut thinking, &mut thinking_signature, &mut blocks);
+                text.push_str(&delta);
+            }
+            AssistantEvent::ThinkingDelta(delta) => {
+                flush_text_block(&mut text, &mut blocks);
+                thinking.push_str(&delta);
+            }
+            AssistantEvent::ThinkingSignature(signature) => thinking_signature = Some(signature),
             AssistantEvent::ToolUse { id, name, input } => {
                 flush_text_block(&mut text, &mut blocks);
+                flush_thinking_block(&mut thinking, &mut thinking_signature, &mut blocks);
                 blocks.push(ContentBlock::ToolUse { id, name, input });
             }
             AssistantEvent::Usage(value) => usage = Some(value),
@@ -266,6 +279,7 @@ fn build_assistant_message(
     }
 
     flush_text_block(&mut text, &mut blocks);
+    flush_thinking_block(&mut thinking, &mut thinking_signature, &mut blocks);
 
     if !finished {
         return Err(RuntimeError::new(
@@ -290,6 +304,19 @@ fn flush_text_block(text: &mut String, blocks: &mut Vec<ContentBlock>) {
     }
 }
 
+fn flush_thinking_block(
+    thinking: &mut String,
+    signature: &mut Option<String>,
+    blocks: &mut Vec<ContentBlock>,
+) {
+    if !thinking.is_empty() || signature.is_some() {
+        blocks.push(ContentBlock::Thinking {
+            text: std::mem::take(thinking),
+            signature: signature.take(),
+        });
+    }
+}
+
 type ToolHandler = Box<dyn FnMut(&str) -> Result<String, ToolError>>;
 
 #[derive(Default)]
@@ -325,8 +352,8 @@ impl ToolExecutor for StaticToolExecutor {
 #[cfg(test)]
 mod tests {
     use super::{
-        ApiClient, ApiRequest, AssistantEvent, ConversationRuntime, RuntimeError,
-        StaticToolExecutor,
+        build_assistant_message, ApiClient, ApiRequest, AssistantEvent, ConversationRuntime,
+        RuntimeError, StaticToolExecutor,
     };
     use crate::compact::CompactionConfig;
     use crate::permissions::{
@@ -408,7 +435,7 @@ mod tests {
                 .sum::<i32>();
             Ok(total.to_string())
         });
-        let permission_policy = PermissionPolicy::new(PermissionMode::Prompt);
+        let permission_policy = PermissionPolicy::new(PermissionMode::WorkspaceWrite);
         let system_prompt = SystemPromptBuilder::new()
             .with_project_context(ProjectContext {
                 cwd: PathBuf::from("/tmp/project"),
@@ -487,7 +514,7 @@ mod tests {
             Session::new(),
             SingleCallApiClient,
             StaticToolExecutor::new(),
-            PermissionPolicy::new(PermissionMode::Prompt),
+            PermissionPolicy::new(PermissionMode::WorkspaceWrite),
             vec!["system".to_string()],
         );
 
@@ -502,6 +529,29 @@ mod tests {
         ));
     }
 
+    #[test]
+    fn thinking_blocks_are_preserved_separately_from_text() {
+        let (message, usage) = build_assistant_message(vec![
+            AssistantEvent::ThinkingDelta("first ".to_string()),
+            AssistantEvent::ThinkingDelta("second".to_string()),
+            AssistantEvent::ThinkingSignature("sig-1".to_string()),
+            AssistantEvent::TextDelta("final".to_string()),
+            AssistantEvent::MessageStop,
+        ])
+        .expect("assistant message should build");
+
+        assert_eq!(usage, None);
+        assert!(matches!(
+            &message.blocks[0],
+            ContentBlock::Thinking { text, signature }
+                if text == "first second" && signature.as_deref() == Some("sig-1")
+        ));
+        assert!(matches!(
+            &message.blocks[1],
+            ContentBlock::Text { text } if text == "final"
+        ));
+    }
+
     #[test]
     fn reconstructs_usage_tracker_from_restored_session() {
         struct SimpleApi;
@@ -536,7 +586,7 @@ mod tests {
             session,
             SimpleApi,
             StaticToolExecutor::new(),
-            PermissionPolicy::new(PermissionMode::Allow),
+            PermissionPolicy::new(PermissionMode::DangerFullAccess),
             vec!["system".to_string()],
         );
 
@@ -563,7 +613,7 @@ mod tests {
             Session::new(),
             SimpleApi,
             StaticToolExecutor::new(),
-            PermissionPolicy::new(PermissionMode::Allow),
+            PermissionPolicy::new(PermissionMode::DangerFullAccess),
             vec!["system".to_string()],
         );
         runtime.run_turn("a", None).expect("turn a");

rust/crates/runtime/src/permissions.rs

@@ -1,16 +1,29 @@
 use std::collections::BTreeMap;
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
 pub enum PermissionMode {
-    Allow,
-    Deny,
-    Prompt,
+    ReadOnly,
+    WorkspaceWrite,
+    DangerFullAccess,
+}
+
+impl PermissionMode {
+    #[must_use]
+    pub fn as_str(self) -> &'static str {
+        match self {
+            Self::ReadOnly => "read-only",
+            Self::WorkspaceWrite => "workspace-write",
+            Self::DangerFullAccess => "danger-full-access",
+        }
+    }
 }
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct PermissionRequest {
     pub tool_name: String,
     pub input: String,
+    pub current_mode: PermissionMode,
+    pub required_mode: PermissionMode,
 }
 
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -31,31 +44,41 @@ pub enum PermissionOutcome {
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct PermissionPolicy {
-    default_mode: PermissionMode,
-    tool_modes: BTreeMap<String, PermissionMode>,
+    active_mode: PermissionMode,
+    tool_requirements: BTreeMap<String, PermissionMode>,
 }
 
 impl PermissionPolicy {
     #[must_use]
-    pub fn new(default_mode: PermissionMode) -> Self {
+    pub fn new(active_mode: PermissionMode) -> Self {
         Self {
-            default_mode,
-            tool_modes: BTreeMap::new(),
+            active_mode,
+            tool_requirements: BTreeMap::new(),
         }
     }
 
     #[must_use]
-    pub fn with_tool_mode(mut self, tool_name: impl Into<String>, mode: PermissionMode) -> Self {
-        self.tool_modes.insert(tool_name.into(), mode);
+    pub fn with_tool_requirement(
+        mut self,
+        tool_name: impl Into<String>,
+        required_mode: PermissionMode,
+    ) -> Self {
+        self.tool_requirements
+            .insert(tool_name.into(), required_mode);
         self
     }
 
     #[must_use]
-    pub fn mode_for(&self, tool_name: &str) -> PermissionMode {
-        self.tool_modes
+    pub fn active_mode(&self) -> PermissionMode {
+        self.active_mode
+    }
+
+    #[must_use]
+    pub fn required_mode_for(&self, tool_name: &str) -> PermissionMode {
+        self.tool_requirements
             .get(tool_name)
             .copied()
-            .unwrap_or(self.default_mode)
+            .unwrap_or(PermissionMode::DangerFullAccess)
     }
 
     #[must_use]
@@ -65,23 +88,43 @@ impl PermissionPolicy {
         input: &str,
         mut prompter: Option<&mut dyn PermissionPrompter>,
     ) -> PermissionOutcome {
-        match self.mode_for(tool_name) {
-            PermissionMode::Allow => PermissionOutcome::Allow,
-            PermissionMode::Deny => PermissionOutcome::Deny {
-                reason: format!("tool '{tool_name}' denied by permission policy"),
-            },
-            PermissionMode::Prompt => match prompter.as_mut() {
-                Some(prompter) => match prompter.decide(&PermissionRequest {
-                    tool_name: tool_name.to_string(),
-                    input: input.to_string(),
-                }) {
+        let current_mode = self.active_mode();
+        let required_mode = self.required_mode_for(tool_name);
+        if current_mode >= required_mode {
+            return PermissionOutcome::Allow;
+        }
+
+        let request = PermissionRequest {
+            tool_name: tool_name.to_string(),
+            input: input.to_string(),
+            current_mode,
+            required_mode,
+        };
+
+        if current_mode == PermissionMode::WorkspaceWrite
+            && required_mode == PermissionMode::DangerFullAccess
+        {
+            return match prompter.as_mut() {
+                Some(prompter) => match prompter.decide(&request) {
                     PermissionPromptDecision::Allow => PermissionOutcome::Allow,
                     PermissionPromptDecision::Deny { reason } => PermissionOutcome::Deny { reason },
                 },
                 None => PermissionOutcome::Deny {
-                    reason: format!("tool '{tool_name}' requires interactive approval"),
+                    reason: format!(
+                        "tool '{tool_name}' requires approval to escalate from {} to {}",
+                        current_mode.as_str(),
+                        required_mode.as_str()
+                    ),
                 },
-            },
+            };
+        }
+
+        PermissionOutcome::Deny {
+            reason: format!(
+                "tool '{tool_name}' requires {} permission; current mode is {}",
+                required_mode.as_str(),
+                current_mode.as_str()
+            ),
         }
     }
 }
@@ -93,25 +136,92 @@ mod tests {
         PermissionPrompter, PermissionRequest,
     };
 
-    struct AllowPrompter;
+    struct RecordingPrompter {
+        seen: Vec<PermissionRequest>,
+        allow: bool,
+    }
 
-    impl PermissionPrompter for AllowPrompter {
+    impl PermissionPrompter for RecordingPrompter {
         fn decide(&mut self, request: &PermissionRequest) -> PermissionPromptDecision {
-            assert_eq!(request.tool_name, "bash");
-            PermissionPromptDecision::Allow
+            self.seen.push(request.clone());
+            if self.allow {
+                PermissionPromptDecision::Allow
+            } else {
+                PermissionPromptDecision::Deny {
+                    reason: "not now".to_string(),
+                }
+            }
         }
     }
 
     #[test]
-    fn uses_tool_specific_overrides() {
-        let policy = PermissionPolicy::new(PermissionMode::Deny)
-            .with_tool_mode("bash", PermissionMode::Prompt);
+    fn allows_tools_when_active_mode_meets_requirement() {
+        let policy = PermissionPolicy::new(PermissionMode::WorkspaceWrite)
+            .with_tool_requirement("read_file", PermissionMode::ReadOnly)
+            .with_tool_requirement("write_file", PermissionMode::WorkspaceWrite);
+
+        assert_eq!(
+            policy.authorize("read_file", "{}", None),
+            PermissionOutcome::Allow
+        );
+        assert_eq!(
+            policy.authorize("write_file", "{}", None),
+            PermissionOutcome::Allow
+        );
+    }
+
+    #[test]
+    fn denies_read_only_escalations_without_prompt() {
+        let policy = PermissionPolicy::new(PermissionMode::ReadOnly)
+            .with_tool_requirement("write_file", PermissionMode::WorkspaceWrite)
+            .with_tool_requirement("bash", PermissionMode::DangerFullAccess);
 
-        let outcome = policy.authorize("bash", "echo hi", Some(&mut AllowPrompter));
-        assert_eq!(outcome, PermissionOutcome::Allow);
         assert!(matches!(
-            policy.authorize("edit", "x", None),
-            PermissionOutcome::Deny { .. }
+            policy.authorize("write_file", "{}", None),
+            PermissionOutcome::Deny { reason } if reason.contains("requires workspace-write permission")
+        ));
+        assert!(matches!(
+            policy.authorize("bash", "{}", None),
+            PermissionOutcome::Deny { reason } if reason.contains("requires danger-full-access permission")
+        ));
+    }
+
+    #[test]
+    fn prompts_for_workspace_write_to_danger_full_access_escalation() {
+        let policy = PermissionPolicy::new(PermissionMode::WorkspaceWrite)
+            .with_tool_requirement("bash", PermissionMode::DangerFullAccess);
+        let mut prompter = RecordingPrompter {
+            seen: Vec::new(),
+            allow: true,
+        };
+
+        let outcome = policy.authorize("bash", "echo hi", Some(&mut prompter));
+
+        assert_eq!(outcome, PermissionOutcome::Allow);
+        assert_eq!(prompter.seen.len(), 1);
+        assert_eq!(prompter.seen[0].tool_name, "bash");
+        assert_eq!(
+            prompter.seen[0].current_mode,
+            PermissionMode::WorkspaceWrite
+        );
+        assert_eq!(
+            prompter.seen[0].required_mode,
+            PermissionMode::DangerFullAccess
+        );
+    }
+
+    #[test]
+    fn honors_prompt_rejection_reason() {
+        let policy = PermissionPolicy::new(PermissionMode::WorkspaceWrite)
+            .with_tool_requirement("bash", PermissionMode::DangerFullAccess);
+        let mut prompter = RecordingPrompter {
+            seen: Vec::new(),
+            allow: false,
+        };
+
+        assert!(matches!(
+            policy.authorize("bash", "echo hi", Some(&mut prompter)),
+            PermissionOutcome::Deny { reason } if reason == "not now"
         ));
     }
 }

rust/crates/runtime/src/session.rs

@@ -19,6 +19,10 @@ pub enum ContentBlock {
     Text {
         text: String,
     },
+    Thinking {
+        text: String,
+        signature: Option<String>,
+    },
     ToolUse {
         id: String,
         name: String,
@@ -257,6 +261,19 @@ impl ContentBlock {
                 object.insert("type".to_string(), JsonValue::String("text".to_string()));
                 object.insert("text".to_string(), JsonValue::String(text.clone()));
             }
+            Self::Thinking { text, signature } => {
+                object.insert(
+                    "type".to_string(),
+                    JsonValue::String("thinking".to_string()),
+                );
+                object.insert("text".to_string(), JsonValue::String(text.clone()));
+                if let Some(signature) = signature {
+                    object.insert(
+                        "signature".to_string(),
+                        JsonValue::String(signature.clone()),
+                    );
+                }
+            }
             Self::ToolUse { id, name, input } => {
                 object.insert(
                     "type".to_string(),
@@ -303,6 +320,13 @@ impl ContentBlock {
             "text" => Ok(Self::Text {
                 text: required_string(object, "text")?,
             }),
+            "thinking" => Ok(Self::Thinking {
+                text: required_string(object, "text")?,
+                signature: object
+                    .get("signature")
+                    .and_then(JsonValue::as_str)
+                    .map(ToOwned::to_owned),
+            }),
             "tool_use" => Ok(Self::ToolUse {
                 id: required_string(object, "id")?,
                 name: required_string(object, "name")?,

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

@@ -2,7 +2,7 @@ use std::io::{self, Write};
 use std::path::PathBuf;
 
 use crate::args::{OutputFormat, PermissionMode};
-use crate::input::LineEditor;
+use crate::input::{LineEditor, ReadOutcome};
 use crate::render::{Spinner, TerminalRenderer};
 use runtime::{ConversationClient, ConversationMessage, RuntimeError, StreamEvent, UsageSummary};
 
@@ -111,16 +111,21 @@ impl CliApp {
     }
 
     pub fn run_repl(&mut self) -> io::Result<()> {
-        let editor = LineEditor::new("› ");
+        let mut editor = LineEditor::new("› ", Vec::new());
         println!("Rusty Claude CLI interactive mode");
         println!("Type /help for commands. Shift+Enter or Ctrl+J inserts a newline.");
 
-        while let Some(input) = editor.read_line()? {
-            if input.trim().is_empty() {
-                continue;
+        loop {
+            match editor.read_line()? {
+                ReadOutcome::Submit(input) => {
+                    if input.trim().is_empty() {
+                        continue;
+                    }
+                    self.handle_submission(&input, &mut io::stdout())?;
+                }
+                ReadOutcome::Cancel => continue,
+                ReadOutcome::Exit => break,
             }
-
-            self.handle_submission(&input, &mut io::stdout())?;
         }
 
         Ok(())

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

@@ -1,9 +1,8 @@
 use std::io::{self, IsTerminal, Write};
 
-use crossterm::cursor::MoveToColumn;
+use crossterm::cursor::{MoveDown, MoveToColumn, MoveUp};
 use crossterm::event::{self, Event, KeyCode, KeyEvent, KeyModifiers};
 use crossterm::queue;
-use crossterm::style::Print;
 use crossterm::terminal::{disable_raw_mode, enable_raw_mode, Clear, ClearType};
 
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -85,21 +84,124 @@ impl InputBuffer {
         self.buffer.clear();
         self.cursor = 0;
     }
+
+    pub fn replace(&mut self, value: impl Into<String>) {
+        self.buffer = value.into();
+        self.cursor = self.buffer.len();
+    }
+
+    #[must_use]
+    fn current_command_prefix(&self) -> Option<&str> {
+        if self.cursor != self.buffer.len() {
+            return None;
+        }
+        let prefix = &self.buffer[..self.cursor];
+        if prefix.contains(char::is_whitespace) || !prefix.starts_with('/') {
+            return None;
+        }
+        Some(prefix)
+    }
+
+    pub fn complete_slash_command(&mut self, candidates: &[String]) -> bool {
+        let Some(prefix) = self.current_command_prefix() else {
+            return false;
+        };
+
+        let matches = candidates
+            .iter()
+            .filter(|candidate| candidate.starts_with(prefix))
+            .map(String::as_str)
+            .collect::<Vec<_>>();
+        if matches.is_empty() {
+            return false;
+        }
+
+        let replacement = longest_common_prefix(&matches);
+        if replacement == prefix {
+            return false;
+        }
+
+        self.replace(replacement);
+        true
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct RenderedBuffer {
+    lines: Vec<String>,
+    cursor_row: u16,
+    cursor_col: u16,
+}
+
+impl RenderedBuffer {
+    #[must_use]
+    pub fn line_count(&self) -> usize {
+        self.lines.len()
+    }
+
+    fn write(&self, out: &mut impl Write) -> io::Result<()> {
+        for (index, line) in self.lines.iter().enumerate() {
+            if index > 0 {
+                writeln!(out)?;
+            }
+            write!(out, "{line}")?;
+        }
+        Ok(())
+    }
+
+    #[cfg(test)]
+    #[must_use]
+    pub fn lines(&self) -> &[String] {
+        &self.lines
+    }
+
+    #[cfg(test)]
+    #[must_use]
+    pub fn cursor_position(&self) -> (u16, u16) {
+        (self.cursor_row, self.cursor_col)
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum ReadOutcome {
+    Submit(String),
+    Cancel,
+    Exit,
 }
 
 pub struct LineEditor {
     prompt: String,
+    continuation_prompt: String,
+    history: Vec<String>,
+    history_index: Option<usize>,
+    draft: Option<String>,
+    completions: Vec<String>,
 }
 
 impl LineEditor {
     #[must_use]
-    pub fn new(prompt: impl Into<String>) -> Self {
+    pub fn new(prompt: impl Into<String>, completions: Vec<String>) -> Self {
         Self {
             prompt: prompt.into(),
+            continuation_prompt: String::from("> "),
+            history: Vec::new(),
+            history_index: None,
+            draft: None,
+            completions,
         }
     }
 
-    pub fn read_line(&self) -> io::Result<Option<String>> {
+    pub fn push_history(&mut self, entry: impl Into<String>) {
+        let entry = entry.into();
+        if entry.trim().is_empty() {
+            return;
+        }
+        self.history.push(entry);
+        self.history_index = None;
+        self.draft = None;
+    }
+
+    pub fn read_line(&mut self) -> io::Result<ReadOutcome> {
         if !io::stdin().is_terminal() || !io::stdout().is_terminal() {
             return self.read_line_fallback();
         }
@@ -107,29 +209,43 @@ impl LineEditor {
         enable_raw_mode()?;
         let mut stdout = io::stdout();
         let mut input = InputBuffer::new();
-        self.redraw(&mut stdout, &input)?;
+        let mut rendered_lines = 1usize;
+        self.redraw(&mut stdout, &input, rendered_lines)?;
 
         loop {
             let event = event::read()?;
             if let Event::Key(key) = event {
-                match Self::handle_key(key, &mut input) {
-                    EditorAction::Continue => self.redraw(&mut stdout, &input)?,
+                match self.handle_key(key, &mut input) {
+                    EditorAction::Continue => {
+                        rendered_lines = self.redraw(&mut stdout, &input, rendered_lines)?;
+                    }
                     EditorAction::Submit => {
                         disable_raw_mode()?;
                         writeln!(stdout)?;
-                        return Ok(Some(input.as_str().to_owned()));
+                        self.history_index = None;
+                        self.draft = None;
+                        return Ok(ReadOutcome::Submit(input.as_str().to_owned()));
                     }
                     EditorAction::Cancel => {
                         disable_raw_mode()?;
                         writeln!(stdout)?;
-                        return Ok(None);
+                        self.history_index = None;
+                        self.draft = None;
+                        return Ok(ReadOutcome::Cancel);
+                    }
+                    EditorAction::Exit => {
+                        disable_raw_mode()?;
+                        writeln!(stdout)?;
+                        self.history_index = None;
+                        self.draft = None;
+                        return Ok(ReadOutcome::Exit);
                     }
                 }
             }
         }
     }
 
-    fn read_line_fallback(&self) -> io::Result<Option<String>> {
+    fn read_line_fallback(&self) -> io::Result<ReadOutcome> {
         let mut stdout = io::stdout();
         write!(stdout, "{}", self.prompt)?;
         stdout.flush()?;
@@ -137,22 +253,32 @@ impl LineEditor {
         let mut buffer = String::new();
         let bytes_read = io::stdin().read_line(&mut buffer)?;
         if bytes_read == 0 {
-            return Ok(None);
+            return Ok(ReadOutcome::Exit);
         }
 
         while matches!(buffer.chars().last(), Some('\n' | '\r')) {
             buffer.pop();
         }
-        Ok(Some(buffer))
+        Ok(ReadOutcome::Submit(buffer))
     }
 
-    fn handle_key(key: KeyEvent, input: &mut InputBuffer) -> EditorAction {
+    #[allow(clippy::too_many_lines)]
+    fn handle_key(&mut self, key: KeyEvent, input: &mut InputBuffer) -> EditorAction {
         match key {
             KeyEvent {
                 code: KeyCode::Char('c'),
                 modifiers,
                 ..
-            } if modifiers.contains(KeyModifiers::CONTROL) => EditorAction::Cancel,
+            } if modifiers.contains(KeyModifiers::CONTROL) => {
+                if input.as_str().is_empty() {
+                    EditorAction::Exit
+                } else {
+                    input.clear();
+                    self.history_index = None;
+                    self.draft = None;
+                    EditorAction::Cancel
+                }
+            }
             KeyEvent {
                 code: KeyCode::Char('j'),
                 modifiers,
@@ -194,6 +320,25 @@ impl LineEditor {
                 input.move_right();
                 EditorAction::Continue
             }
+            KeyEvent {
+                code: KeyCode::Up, ..
+            } => {
+                self.navigate_history_up(input);
+                EditorAction::Continue
+            }
+            KeyEvent {
+                code: KeyCode::Down,
+                ..
+            } => {
+                self.navigate_history_down(input);
+                EditorAction::Continue
+            }
+            KeyEvent {
+                code: KeyCode::Tab, ..
+            } => {
+                input.complete_slash_command(&self.completions);
+                EditorAction::Continue
+            }
             KeyEvent {
                 code: KeyCode::Home,
                 ..
@@ -211,6 +356,8 @@ impl LineEditor {
                 code: KeyCode::Esc, ..
             } => {
                 input.clear();
+                self.history_index = None;
+                self.draft = None;
                 EditorAction::Cancel
             }
             KeyEvent {
@@ -219,22 +366,74 @@ impl LineEditor {
                 ..
             } if modifiers.is_empty() || modifiers == KeyModifiers::SHIFT => {
                 input.insert(ch);
+                self.history_index = None;
+                self.draft = None;
                 EditorAction::Continue
             }
             _ => EditorAction::Continue,
         }
     }
 
-    fn redraw(&self, out: &mut impl Write, input: &InputBuffer) -> io::Result<()> {
-        let display = input.as_str().replace('\n', "\\n\n> ");
+    fn navigate_history_up(&mut self, input: &mut InputBuffer) {
+        if self.history.is_empty() {
+            return;
+        }
+
+        match self.history_index {
+            Some(0) => {}
+            Some(index) => {
+                let next_index = index - 1;
+                input.replace(self.history[next_index].clone());
+                self.history_index = Some(next_index);
+            }
+            None => {
+                self.draft = Some(input.as_str().to_owned());
+                let next_index = self.history.len() - 1;
+                input.replace(self.history[next_index].clone());
+                self.history_index = Some(next_index);
+            }
+        }
+    }
+
+    fn navigate_history_down(&mut self, input: &mut InputBuffer) {
+        let Some(index) = self.history_index else {
+            return;
+        };
+
+        if index + 1 < self.history.len() {
+            let next_index = index + 1;
+            input.replace(self.history[next_index].clone());
+            self.history_index = Some(next_index);
+            return;
+        }
+
+        input.replace(self.draft.take().unwrap_or_default());
+        self.history_index = None;
+    }
+
+    fn redraw(
+        &self,
+        out: &mut impl Write,
+        input: &InputBuffer,
+        previous_line_count: usize,
+    ) -> io::Result<usize> {
+        let rendered = render_buffer(&self.prompt, &self.continuation_prompt, input);
+        if previous_line_count > 1 {
+            queue!(out, MoveUp(saturating_u16(previous_line_count - 1)))?;
+        }
+        queue!(out, MoveToColumn(0), Clear(ClearType::FromCursorDown),)?;
+        rendered.write(out)?;
         queue!(
             out,
+            MoveUp(saturating_u16(rendered.line_count().saturating_sub(1))),
             MoveToColumn(0),
-            Clear(ClearType::CurrentLine),
-            Print(&self.prompt),
-            Print(display),
         )?;
-        out.flush()
+        if rendered.cursor_row > 0 {
+            queue!(out, MoveDown(rendered.cursor_row))?;
+        }
+        queue!(out, MoveToColumn(rendered.cursor_col))?;
+        out.flush()?;
+        Ok(rendered.line_count())
     }
 }
 
@@ -243,11 +442,76 @@ enum EditorAction {
     Continue,
     Submit,
     Cancel,
+    Exit,
+}
+
+#[must_use]
+pub fn render_buffer(
+    prompt: &str,
+    continuation_prompt: &str,
+    input: &InputBuffer,
+) -> RenderedBuffer {
+    let before_cursor = &input.as_str()[..input.cursor];
+    let cursor_row = saturating_u16(before_cursor.chars().filter(|ch| *ch == '\n').count());
+    let cursor_line = before_cursor.rsplit('\n').next().unwrap_or_default();
+    let cursor_prompt = if cursor_row == 0 {
+        prompt
+    } else {
+        continuation_prompt
+    };
+    let cursor_col = saturating_u16(cursor_prompt.chars().count() + cursor_line.chars().count());
+
+    let mut lines = Vec::new();
+    for (index, line) in input.as_str().split('\n').enumerate() {
+        let prefix = if index == 0 {
+            prompt
+        } else {
+            continuation_prompt
+        };
+        lines.push(format!("{prefix}{line}"));
+    }
+    if lines.is_empty() {
+        lines.push(prompt.to_string());
+    }
+
+    RenderedBuffer {
+        lines,
+        cursor_row,
+        cursor_col,
+    }
+}
+
+#[must_use]
+fn longest_common_prefix(values: &[&str]) -> String {
+    let Some(first) = values.first() else {
+        return String::new();
+    };
+
+    let mut prefix = (*first).to_string();
+    for value in values.iter().skip(1) {
+        while !value.starts_with(&prefix) {
+            prefix.pop();
+            if prefix.is_empty() {
+                break;
+            }
+        }
+    }
+    prefix
+}
+
+#[must_use]
+fn saturating_u16(value: usize) -> u16 {
+    u16::try_from(value).unwrap_or(u16::MAX)
 }
 
 #[cfg(test)]
 mod tests {
-    use super::InputBuffer;
+    use super::{render_buffer, InputBuffer, LineEditor};
+    use crossterm::event::{KeyCode, KeyEvent, KeyModifiers};
+
+    fn key(code: KeyCode) -> KeyEvent {
+        KeyEvent::new(code, KeyModifiers::NONE)
+    }
 
     #[test]
     fn supports_basic_line_editing() {
@@ -266,4 +530,119 @@ mod tests {
         assert_eq!(input.as_str(), "hix");
         assert_eq!(input.cursor(), 2);
     }
+
+    #[test]
+    fn completes_unique_slash_command() {
+        let mut input = InputBuffer::new();
+        for ch in "/he".chars() {
+            input.insert(ch);
+        }
+
+        assert!(input.complete_slash_command(&[
+            "/help".to_string(),
+            "/hello".to_string(),
+            "/status".to_string(),
+        ]));
+        assert_eq!(input.as_str(), "/hel");
+
+        assert!(input.complete_slash_command(&["/help".to_string(), "/status".to_string()]));
+        assert_eq!(input.as_str(), "/help");
+    }
+
+    #[test]
+    fn ignores_completion_when_prefix_is_not_a_slash_command() {
+        let mut input = InputBuffer::new();
+        for ch in "hello".chars() {
+            input.insert(ch);
+        }
+
+        assert!(!input.complete_slash_command(&["/help".to_string()]));
+        assert_eq!(input.as_str(), "hello");
+    }
+
+    #[test]
+    fn history_navigation_restores_current_draft() {
+        let mut editor = LineEditor::new("› ", vec![]);
+        editor.push_history("/help");
+        editor.push_history("status report");
+
+        let mut input = InputBuffer::new();
+        for ch in "draft".chars() {
+            input.insert(ch);
+        }
+
+        let _ = editor.handle_key(key(KeyCode::Up), &mut input);
+        assert_eq!(input.as_str(), "status report");
+
+        let _ = editor.handle_key(key(KeyCode::Up), &mut input);
+        assert_eq!(input.as_str(), "/help");
+
+        let _ = editor.handle_key(key(KeyCode::Down), &mut input);
+        assert_eq!(input.as_str(), "status report");
+
+        let _ = editor.handle_key(key(KeyCode::Down), &mut input);
+        assert_eq!(input.as_str(), "draft");
+    }
+
+    #[test]
+    fn tab_key_completes_from_editor_candidates() {
+        let mut editor = LineEditor::new(
+            "› ",
+            vec![
+                "/help".to_string(),
+                "/status".to_string(),
+                "/session".to_string(),
+            ],
+        );
+        let mut input = InputBuffer::new();
+        for ch in "/st".chars() {
+            input.insert(ch);
+        }
+
+        let _ = editor.handle_key(key(KeyCode::Tab), &mut input);
+        assert_eq!(input.as_str(), "/status");
+    }
+
+    #[test]
+    fn renders_multiline_buffers_with_continuation_prompt() {
+        let mut input = InputBuffer::new();
+        for ch in "hello\nworld".chars() {
+            if ch == '\n' {
+                input.insert_newline();
+            } else {
+                input.insert(ch);
+            }
+        }
+
+        let rendered = render_buffer("› ", "> ", &input);
+        assert_eq!(
+            rendered.lines(),
+            &["› hello".to_string(), "> world".to_string()]
+        );
+        assert_eq!(rendered.cursor_position(), (1, 7));
+    }
+
+    #[test]
+    fn ctrl_c_exits_only_when_buffer_is_empty() {
+        let mut editor = LineEditor::new("› ", vec![]);
+        let mut empty = InputBuffer::new();
+        assert!(matches!(
+            editor.handle_key(
+                KeyEvent::new(KeyCode::Char('c'), KeyModifiers::CONTROL),
+                &mut empty,
+            ),
+            super::EditorAction::Exit
+        ));
+
+        let mut filled = InputBuffer::new();
+        filled.insert('x');
+        assert!(matches!(
+            editor.handle_key(
+                KeyEvent::new(KeyCode::Char('c'), KeyModifiers::CONTROL),
+                &mut filled,
+            ),
+            super::EditorAction::Cancel
+        ));
+        assert!(filled.as_str().is_empty());
+    }
 }

rust/crates/tools/src/lib.rs

@@ -6,7 +6,7 @@ use std::time::{Duration, Instant};
 use reqwest::blocking::Client;
 use runtime::{
     edit_file, execute_bash, glob_search, grep_search, read_file, write_file, BashCommandInput,
-    GrepSearchInput,
+    GrepSearchInput, PermissionMode,
 };
 use serde::{Deserialize, Serialize};
 use serde_json::{json, Value};
@@ -45,6 +45,7 @@ pub struct ToolSpec {
     pub name: &'static str,
     pub description: &'static str,
     pub input_schema: Value,
+    pub required_permission: PermissionMode,
 }
 
 #[must_use]
@@ -66,6 +67,7 @@ pub fn mvp_tool_specs() -> Vec<ToolSpec> {
                 "required": ["command"],
                 "additionalProperties": false
             }),
+            required_permission: PermissionMode::DangerFullAccess,
         },
         ToolSpec {
             name: "read_file",
@@ -80,6 +82,7 @@ pub fn mvp_tool_specs() -> Vec<ToolSpec> {
                 "required": ["path"],
                 "additionalProperties": false
             }),
+            required_permission: PermissionMode::ReadOnly,
         },
         ToolSpec {
             name: "write_file",
@@ -93,6 +96,7 @@ pub fn mvp_tool_specs() -> Vec<ToolSpec> {
                 "required": ["path", "content"],
                 "additionalProperties": false
             }),
+            required_permission: PermissionMode::WorkspaceWrite,
         },
         ToolSpec {
             name: "edit_file",
@@ -108,6 +112,7 @@ pub fn mvp_tool_specs() -> Vec<ToolSpec> {
                 "required": ["path", "old_string", "new_string"],
                 "additionalProperties": false
             }),
+            required_permission: PermissionMode::WorkspaceWrite,
         },
         ToolSpec {
             name: "glob_search",
@@ -121,6 +126,7 @@ pub fn mvp_tool_specs() -> Vec<ToolSpec> {
                 "required": ["pattern"],
                 "additionalProperties": false
             }),
+            required_permission: PermissionMode::ReadOnly,
         },
         ToolSpec {
             name: "grep_search",
@@ -146,6 +152,7 @@ pub fn mvp_tool_specs() -> Vec<ToolSpec> {
                 "required": ["pattern"],
                 "additionalProperties": false
             }),
+            required_permission: PermissionMode::ReadOnly,
         },
         ToolSpec {
             name: "WebFetch",
@@ -160,6 +167,7 @@ pub fn mvp_tool_specs() -> Vec<ToolSpec> {
                 "required": ["url", "prompt"],
                 "additionalProperties": false
             }),
+            required_permission: PermissionMode::ReadOnly,
         },
         ToolSpec {
             name: "WebSearch",
@@ -180,6 +188,7 @@ pub fn mvp_tool_specs() -> Vec<ToolSpec> {
                 "required": ["query"],
                 "additionalProperties": false
             }),
+            required_permission: PermissionMode::ReadOnly,
         },
         ToolSpec {
             name: "TodoWrite",
@@ -207,6 +216,7 @@ pub fn mvp_tool_specs() -> Vec<ToolSpec> {
                 "required": ["todos"],
                 "additionalProperties": false
             }),
+            required_permission: PermissionMode::WorkspaceWrite,
         },
         ToolSpec {
             name: "Skill",
@@ -220,6 +230,7 @@ pub fn mvp_tool_specs() -> Vec<ToolSpec> {
                 "required": ["skill"],
                 "additionalProperties": false
             }),
+            required_permission: PermissionMode::ReadOnly,
         },
         ToolSpec {
             name: "Agent",
@@ -236,6 +247,7 @@ pub fn mvp_tool_specs() -> Vec<ToolSpec> {
                 "required": ["description", "prompt"],
                 "additionalProperties": false
             }),
+            required_permission: PermissionMode::DangerFullAccess,
         },
         ToolSpec {
             name: "ToolSearch",
@@ -249,6 +261,7 @@ pub fn mvp_tool_specs() -> Vec<ToolSpec> {
                 "required": ["query"],
                 "additionalProperties": false
             }),
+            required_permission: PermissionMode::ReadOnly,
         },
         ToolSpec {
             name: "NotebookEdit",
@@ -265,6 +278,7 @@ pub fn mvp_tool_specs() -> Vec<ToolSpec> {
                 "required": ["notebook_path"],
                 "additionalProperties": false
             }),
+            required_permission: PermissionMode::WorkspaceWrite,
         },
         ToolSpec {
             name: "Sleep",
@@ -277,6 +291,7 @@ pub fn mvp_tool_specs() -> Vec<ToolSpec> {
                 "required": ["duration_ms"],
                 "additionalProperties": false
             }),
+            required_permission: PermissionMode::ReadOnly,
         },
         ToolSpec {
             name: "SendUserMessage",
@@ -297,6 +312,7 @@ pub fn mvp_tool_specs() -> Vec<ToolSpec> {
                 "required": ["message", "status"],
                 "additionalProperties": false
             }),
+            required_permission: PermissionMode::ReadOnly,
         },
         ToolSpec {
             name: "Config",
@@ -312,6 +328,7 @@ pub fn mvp_tool_specs() -> Vec<ToolSpec> {
                 "required": ["setting"],
                 "additionalProperties": false
             }),
+            required_permission: PermissionMode::WorkspaceWrite,
         },
         ToolSpec {
             name: "StructuredOutput",
@@ -320,6 +337,7 @@ pub fn mvp_tool_specs() -> Vec<ToolSpec> {
                 "type": "object",
                 "additionalProperties": true
             }),
+            required_permission: PermissionMode::ReadOnly,
         },
         ToolSpec {
             name: "REPL",
@@ -334,6 +352,7 @@ pub fn mvp_tool_specs() -> Vec<ToolSpec> {
                 "required": ["code", "language"],
                 "additionalProperties": false
             }),
+            required_permission: PermissionMode::DangerFullAccess,
         },
         ToolSpec {
             name: "PowerShell",
@@ -349,6 +368,7 @@ pub fn mvp_tool_specs() -> Vec<ToolSpec> {
                 "required": ["command"],
                 "additionalProperties": false
             }),
+            required_permission: PermissionMode::DangerFullAccess,
         },
     ]
 }