Make local environment failures diagnosable from the CLI

Add a non-interactive doctor subcommand that checks API key reachability, OAuth credential state, config files, git, MCP servers, network access, and system metadata in one structured report. The implementation reuses existing runtime/auth plumbing and adds focused tests for parsing and report behavior.

Also update stale runtime permission-mode tests so workspace verification reflects the current enum model rather than historical Prompt/Allow variants.

Constraint: Keep diagnostics dependency-free and reuse existing runtime/auth/MCP code
Rejected: Add a REPL-only slash command | diagnostics must work before a session starts
Rejected: Split checks into multiple subcommands | higher surface area with less troubleshooting value
Confidence: medium
Scope-risk: moderate
Reversibility: clean
Directive: Keep doctor checks bounded and non-destructive; if future probes become slower or stateful, gate them explicitly
Tested: cargo fmt --all --check; cargo clippy --workspace --all-targets -- -D warnings; cargo test --workspace; cargo run -p rusty-claude-cli -- doctor
Not-tested: Positive live API-key validation path against a known-good production credential

rust/crates/runtime/src/conversation.rs

@@ -408,7 +408,7 @@ 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 +487,7 @@ mod tests {
             Session::new(),
             SingleCallApiClient,
             StaticToolExecutor::new(),
-            PermissionPolicy::new(PermissionMode::Prompt),
+            PermissionPolicy::new(PermissionMode::WorkspaceWrite),
             vec!["system".to_string()],
         );
 
@@ -536,7 +536,7 @@ mod tests {
             session,
             SimpleApi,
             StaticToolExecutor::new(),
-            PermissionPolicy::new(PermissionMode::Allow),
+            PermissionPolicy::new(PermissionMode::DangerFullAccess),
             vec!["system".to_string()],
         );
 
@@ -563,7 +563,7 @@ 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/rusty-claude-cli/src/main.rs

@@ -5,15 +5,16 @@ use std::collections::{BTreeMap, BTreeSet};
 use std::env;
 use std::fs;
 use std::io::{self, Read, Write};
-use std::net::TcpListener;
+use std::net::{TcpListener, TcpStream, ToSocketAddrs};
 use std::path::{Path, PathBuf};
 use std::process::Command;
-use std::time::{SystemTime, UNIX_EPOCH};
+use std::time::{Duration, SystemTime, UNIX_EPOCH};
 
 use api::{
-    resolve_startup_auth_source, AnthropicClient, AuthSource, ContentBlockDelta, InputContentBlock,
-    InputMessage, MessageRequest, MessageResponse, OutputContentBlock,
-    StreamEvent as ApiStreamEvent, ToolChoice, ToolDefinition, ToolResultContentBlock,
+    oauth_token_is_expired, resolve_startup_auth_source, AnthropicClient, ApiError, AuthSource,
+    ContentBlockDelta, InputContentBlock, InputMessage, MessageRequest, MessageResponse,
+    OutputContentBlock, StreamEvent as ApiStreamEvent, ToolChoice, ToolDefinition,
+    ToolResultContentBlock,
 };
 
 use commands::{
@@ -22,10 +23,11 @@ use commands::{
 use compat_harness::{extract_manifest, UpstreamPaths};
 use render::{Spinner, TerminalRenderer};
 use runtime::{
-    clear_oauth_credentials, generate_pkce_pair, generate_state, load_system_prompt,
-    parse_oauth_callback_request_target, save_oauth_credentials, ApiClient, ApiRequest,
-    AssistantEvent, CompactionConfig, ConfigLoader, ConfigSource, ContentBlock,
-    ConversationMessage, ConversationRuntime, MessageRole, OAuthAuthorizationRequest,
+    clear_oauth_credentials, generate_pkce_pair, generate_state, load_oauth_credentials,
+    load_system_prompt, parse_oauth_callback_request_target, save_oauth_credentials, ApiClient,
+    ApiRequest, AssistantEvent, CompactionConfig, ConfigLoader, ConfigSource, ContentBlock,
+    ConversationMessage, ConversationRuntime, McpClientBootstrap, McpClientTransport,
+    McpServerConfig, McpStdioProcess, MessageRole, OAuthAuthorizationRequest,
     OAuthTokenExchangeRequest, PermissionMode, PermissionPolicy, ProjectContext, RuntimeError,
     Session, TokenUsage, ToolError, ToolExecutor, UsageTracker,
 };
@@ -74,6 +76,7 @@ fn run() -> Result<(), Box<dyn std::error::Error>> {
             .run_turn_with_output(&prompt, output_format)?,
         CliAction::Login => run_login()?,
         CliAction::Logout => run_logout()?,
+        CliAction::Doctor => run_doctor()?,
         CliAction::Repl {
             model,
             allowed_tools,
@@ -106,6 +109,7 @@ enum CliAction {
     },
     Login,
     Logout,
+    Doctor,
     Repl {
         model: String,
         allowed_tools: Option<AllowedToolSet>,
@@ -230,6 +234,7 @@ fn parse_args(args: &[String]) -> Result<CliAction, String> {
         "system-prompt" => parse_system_prompt_args(&rest[1..]),
         "login" => Ok(CliAction::Login),
         "logout" => Ok(CliAction::Logout),
+        "doctor" => Ok(CliAction::Doctor),
         "prompt" => {
             let prompt = rest[1..].join(" ");
             if prompt.trim().is_empty() {
@@ -520,6 +525,627 @@ fn wait_for_oauth_callback(
     Ok(callback)
 }
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum DiagnosticLevel {
+    Ok,
+    Warn,
+    Fail,
+}
+
+impl DiagnosticLevel {
+    const fn label(self) -> &'static str {
+        match self {
+            Self::Ok => "OK",
+            Self::Warn => "WARN",
+            Self::Fail => "FAIL",
+        }
+    }
+
+    const fn is_failure(self) -> bool {
+        matches!(self, Self::Fail)
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+struct DiagnosticCheck {
+    name: &'static str,
+    level: DiagnosticLevel,
+    summary: String,
+    details: Vec<String>,
+}
+
+impl DiagnosticCheck {
+    fn new(name: &'static str, level: DiagnosticLevel, summary: impl Into<String>) -> Self {
+        Self {
+            name,
+            level,
+            summary: summary.into(),
+            details: Vec::new(),
+        }
+    }
+
+    fn with_details(mut self, details: Vec<String>) -> Self {
+        self.details = details;
+        self
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+enum OAuthDiagnosticStatus {
+    Missing,
+    Valid,
+    ExpiredRefreshable,
+    ExpiredNoRefresh,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+struct ConfigFileCheck {
+    path: PathBuf,
+    exists: bool,
+    valid: bool,
+    note: String,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+struct DoctorReport {
+    checks: Vec<DiagnosticCheck>,
+}
+
+impl DoctorReport {
+    fn has_failures(&self) -> bool {
+        self.checks.iter().any(|check| check.level.is_failure())
+    }
+
+    fn render(&self) -> String {
+        let mut lines = vec!["Doctor diagnostics".to_string()];
+        let ok_count = self
+            .checks
+            .iter()
+            .filter(|check| check.level == DiagnosticLevel::Ok)
+            .count();
+        let warn_count = self
+            .checks
+            .iter()
+            .filter(|check| check.level == DiagnosticLevel::Warn)
+            .count();
+        let fail_count = self
+            .checks
+            .iter()
+            .filter(|check| check.level == DiagnosticLevel::Fail)
+            .count();
+        lines.push(format!(
+            "Summary\n  OK               {ok_count}\n  Warnings         {warn_count}\n  Failures         {fail_count}"
+        ));
+        lines.extend(self.checks.iter().map(render_diagnostic_check));
+        lines.join("\n\n")
+    }
+}
+
+fn render_diagnostic_check(check: &DiagnosticCheck) -> String {
+    let mut section = vec![format!(
+        "{}\n  Status           {}\n  Summary          {}",
+        check.name,
+        check.level.label(),
+        check.summary
+    )];
+    if !check.details.is_empty() {
+        section.push("  Details".to_string());
+        section.extend(check.details.iter().map(|detail| format!("    - {detail}")));
+    }
+    section.join("\n")
+}
+
+fn run_doctor() -> Result<(), Box<dyn std::error::Error>> {
+    let cwd = env::current_dir()?;
+    let config_loader = ConfigLoader::default_for(&cwd);
+    let config = config_loader.load();
+    let report = DoctorReport {
+        checks: vec![
+            check_api_key_validity(config.as_ref().ok()),
+            check_oauth_token_status(config.as_ref().ok()),
+            check_config_files(&config_loader, config.as_ref()),
+            check_git_availability(&cwd),
+            check_mcp_server_health(config.as_ref().ok()),
+            check_network_connectivity(),
+            check_system_info(&cwd, config.as_ref().ok()),
+        ],
+    };
+    println!("{}", report.render());
+    if report.has_failures() {
+        return Err("doctor found failing checks".into());
+    }
+    Ok(())
+}
+
+fn check_api_key_validity(config: Option<&runtime::RuntimeConfig>) -> DiagnosticCheck {
+    let api_key = match env::var("ANTHROPIC_API_KEY") {
+        Ok(value) if !value.trim().is_empty() => value,
+        Ok(_) | Err(env::VarError::NotPresent) => {
+            return DiagnosticCheck::new(
+                "API key validity",
+                DiagnosticLevel::Warn,
+                "ANTHROPIC_API_KEY is not set",
+            );
+        }
+        Err(error) => {
+            return DiagnosticCheck::new(
+                "API key validity",
+                DiagnosticLevel::Fail,
+                format!("failed to read ANTHROPIC_API_KEY: {error}"),
+            );
+        }
+    };
+
+    let request = MessageRequest {
+        model: config
+            .and_then(runtime::RuntimeConfig::model)
+            .unwrap_or(DEFAULT_MODEL)
+            .to_string(),
+        max_tokens: 1,
+        messages: vec![InputMessage {
+            role: "user".to_string(),
+            content: vec![InputContentBlock::Text {
+                text: "Reply with OK.".to_string(),
+            }],
+        }],
+        system: None,
+        tools: None,
+        tool_choice: None,
+        stream: false,
+    };
+    let runtime = match tokio::runtime::Runtime::new() {
+        Ok(runtime) => runtime,
+        Err(error) => {
+            return DiagnosticCheck::new(
+                "API key validity",
+                DiagnosticLevel::Fail,
+                format!("failed to create async runtime: {error}"),
+            );
+        }
+    };
+    match runtime
+        .block_on(AnthropicClient::from_auth(AuthSource::ApiKey(api_key)).send_message(&request))
+    {
+        Ok(response) => DiagnosticCheck::new(
+            "API key validity",
+            DiagnosticLevel::Ok,
+            "Anthropic API accepted the configured API key",
+        )
+        .with_details(vec![format!(
+            "request_id={} input_tokens={} output_tokens={}",
+            response.request_id.unwrap_or_else(|| "<none>".to_string()),
+            response.usage.input_tokens,
+            response.usage.output_tokens
+        )]),
+        Err(ApiError::Api { status, .. }) if status.as_u16() == 401 || status.as_u16() == 403 => {
+            DiagnosticCheck::new(
+                "API key validity",
+                DiagnosticLevel::Fail,
+                format!("Anthropic API rejected the API key with HTTP {status}"),
+            )
+        }
+        Err(error) => DiagnosticCheck::new(
+            "API key validity",
+            DiagnosticLevel::Warn,
+            format!("unable to conclusively validate the API key: {error}"),
+        ),
+    }
+}
+
+fn classify_oauth_status() -> Result<(OAuthDiagnosticStatus, Vec<String>), io::Error> {
+    let Some(token_set) = load_oauth_credentials()? else {
+        return Ok((OAuthDiagnosticStatus::Missing, vec![]));
+    };
+    let token = api::OAuthTokenSet {
+        access_token: token_set.access_token.clone(),
+        refresh_token: token_set.refresh_token.clone(),
+        expires_at: token_set.expires_at,
+        scopes: token_set.scopes.clone(),
+    };
+    let details = vec![format!(
+        "expires_at={} refresh_token={} scopes={}",
+        token
+            .expires_at
+            .map_or_else(|| "<none>".to_string(), |value| value.to_string()),
+        if token.refresh_token.is_some() {
+            "present"
+        } else {
+            "absent"
+        },
+        if token.scopes.is_empty() {
+            "<none>".to_string()
+        } else {
+            token.scopes.join(",")
+        }
+    )];
+    let status = if oauth_token_is_expired(&token) {
+        if token.refresh_token.is_some() {
+            OAuthDiagnosticStatus::ExpiredRefreshable
+        } else {
+            OAuthDiagnosticStatus::ExpiredNoRefresh
+        }
+    } else {
+        OAuthDiagnosticStatus::Valid
+    };
+    Ok((status, details))
+}
+
+fn check_oauth_token_status(config: Option<&runtime::RuntimeConfig>) -> DiagnosticCheck {
+    match classify_oauth_status() {
+        Ok((OAuthDiagnosticStatus::Missing, _)) => DiagnosticCheck::new(
+            "OAuth token status",
+            DiagnosticLevel::Warn,
+            "no saved OAuth credentials found",
+        ),
+        Ok((OAuthDiagnosticStatus::Valid, details)) => DiagnosticCheck::new(
+            "OAuth token status",
+            DiagnosticLevel::Ok,
+            "saved OAuth token is present and not expired",
+        )
+        .with_details(details),
+        Ok((OAuthDiagnosticStatus::ExpiredRefreshable, mut details)) => {
+            let refresh_ready = config.and_then(runtime::RuntimeConfig::oauth).is_some();
+            details.push(if refresh_ready {
+                "runtime OAuth config is present for refresh".to_string()
+            } else {
+                "runtime OAuth config is missing for refresh".to_string()
+            });
+            DiagnosticCheck::new(
+                "OAuth token status",
+                if refresh_ready {
+                    DiagnosticLevel::Warn
+                } else {
+                    DiagnosticLevel::Fail
+                },
+                "saved OAuth token is expired but includes a refresh token",
+            )
+            .with_details(details)
+        }
+        Ok((OAuthDiagnosticStatus::ExpiredNoRefresh, details)) => DiagnosticCheck::new(
+            "OAuth token status",
+            DiagnosticLevel::Fail,
+            "saved OAuth token is expired and cannot refresh",
+        )
+        .with_details(details),
+        Err(error) => DiagnosticCheck::new(
+            "OAuth token status",
+            DiagnosticLevel::Fail,
+            format!("failed to read saved OAuth credentials: {error}"),
+        ),
+    }
+}
+
+fn validate_config_file(path: &Path) -> ConfigFileCheck {
+    match fs::read_to_string(path) {
+        Ok(contents) => {
+            if contents.trim().is_empty() {
+                return ConfigFileCheck {
+                    path: path.to_path_buf(),
+                    exists: true,
+                    valid: true,
+                    note: "exists but is empty".to_string(),
+                };
+            }
+            match serde_json::from_str::<serde_json::Value>(&contents) {
+                Ok(serde_json::Value::Object(_)) => ConfigFileCheck {
+                    path: path.to_path_buf(),
+                    exists: true,
+                    valid: true,
+                    note: "valid JSON object".to_string(),
+                },
+                Ok(_) => ConfigFileCheck {
+                    path: path.to_path_buf(),
+                    exists: true,
+                    valid: false,
+                    note: "top-level JSON value is not an object".to_string(),
+                },
+                Err(error) => ConfigFileCheck {
+                    path: path.to_path_buf(),
+                    exists: true,
+                    valid: false,
+                    note: format!("invalid JSON: {error}"),
+                },
+            }
+        }
+        Err(error) if error.kind() == io::ErrorKind::NotFound => ConfigFileCheck {
+            path: path.to_path_buf(),
+            exists: false,
+            valid: true,
+            note: "not present".to_string(),
+        },
+        Err(error) => ConfigFileCheck {
+            path: path.to_path_buf(),
+            exists: true,
+            valid: false,
+            note: format!("unreadable: {error}"),
+        },
+    }
+}
+
+fn check_config_files(
+    config_loader: &ConfigLoader,
+    config: Result<&runtime::RuntimeConfig, &runtime::ConfigError>,
+) -> DiagnosticCheck {
+    let file_checks = config_loader
+        .discover()
+        .into_iter()
+        .map(|entry| validate_config_file(&entry.path))
+        .collect::<Vec<_>>();
+    let existing_count = file_checks.iter().filter(|check| check.exists).count();
+    let invalid_count = file_checks
+        .iter()
+        .filter(|check| check.exists && !check.valid)
+        .count();
+    let mut details = file_checks
+        .iter()
+        .map(|check| format!("{} => {}", check.path.display(), check.note))
+        .collect::<Vec<_>>();
+    match config {
+        Ok(runtime_config) => details.push(format!(
+            "merged load succeeded with {} loaded file(s)",
+            runtime_config.loaded_entries().len()
+        )),
+        Err(error) => details.push(format!("merged load failed: {error}")),
+    }
+    DiagnosticCheck::new(
+        "Config files",
+        if invalid_count > 0 || config.is_err() {
+            DiagnosticLevel::Fail
+        } else if existing_count == 0 {
+            DiagnosticLevel::Warn
+        } else {
+            DiagnosticLevel::Ok
+        },
+        format!(
+            "discovered {} candidate file(s), {} existing, {} invalid",
+            file_checks.len(),
+            existing_count,
+            invalid_count
+        ),
+    )
+    .with_details(details)
+}
+
+fn check_git_availability(cwd: &Path) -> DiagnosticCheck {
+    match Command::new("git").arg("--version").output() {
+        Ok(version_output) if version_output.status.success() => {
+            let version = String::from_utf8_lossy(&version_output.stdout)
+                .trim()
+                .to_string();
+            match Command::new("git")
+                .args(["rev-parse", "--show-toplevel"])
+                .current_dir(cwd)
+                .output()
+            {
+                Ok(root_output) if root_output.status.success() => DiagnosticCheck::new(
+                    "Git availability",
+                    DiagnosticLevel::Ok,
+                    "git is installed and the current directory is inside a repository",
+                )
+                .with_details(vec![
+                    version,
+                    format!(
+                        "repo_root={}",
+                        String::from_utf8_lossy(&root_output.stdout).trim()
+                    ),
+                ]),
+                Ok(_) => DiagnosticCheck::new(
+                    "Git availability",
+                    DiagnosticLevel::Warn,
+                    "git is installed but the current directory is not a repository",
+                )
+                .with_details(vec![version]),
+                Err(error) => DiagnosticCheck::new(
+                    "Git availability",
+                    DiagnosticLevel::Warn,
+                    format!("git is installed but repo detection failed: {error}"),
+                )
+                .with_details(vec![version]),
+            }
+        }
+        Ok(output) => DiagnosticCheck::new(
+            "Git availability",
+            DiagnosticLevel::Fail,
+            format!("git --version exited with status {}", output.status),
+        ),
+        Err(error) => DiagnosticCheck::new(
+            "Git availability",
+            DiagnosticLevel::Fail,
+            format!("failed to execute git: {error}"),
+        ),
+    }
+}
+
+fn check_one_mcp_server(
+    name: &str,
+    server: &runtime::ScopedMcpServerConfig,
+) -> (DiagnosticLevel, String) {
+    match &server.config {
+        McpServerConfig::Stdio(_) => {
+            let bootstrap = McpClientBootstrap::from_scoped_config(name, server);
+            let runtime = match tokio::runtime::Builder::new_current_thread()
+                .enable_all()
+                .build()
+            {
+                Ok(runtime) => runtime,
+                Err(error) => {
+                    return (
+                        DiagnosticLevel::Fail,
+                        format!("{name}: runtime error: {error}"),
+                    )
+                }
+            };
+            let detail = runtime.block_on(async {
+                match tokio::time::timeout(Duration::from_secs(3), async {
+                    let mut process = McpStdioProcess::spawn(match &bootstrap.transport {
+                        McpClientTransport::Stdio(transport) => transport,
+                        _ => unreachable!("stdio bootstrap expected"),
+                    })?;
+                    let result = process
+                        .initialize(
+                            runtime::JsonRpcId::Number(1),
+                            runtime::McpInitializeParams {
+                                protocol_version: "2025-03-26".to_string(),
+                                capabilities: serde_json::Value::Object(serde_json::Map::new()),
+                                client_info: runtime::McpInitializeClientInfo {
+                                    name: "doctor".to_string(),
+                                    version: VERSION.to_string(),
+                                },
+                            },
+                        )
+                        .await;
+                    let _ = process.terminate().await;
+                    result
+                })
+                .await
+                {
+                    Ok(Ok(response)) => {
+                        if let Some(error) = response.error {
+                            (
+                                DiagnosticLevel::Fail,
+                                format!(
+                                    "{name}: initialize JSON-RPC error {} ({})",
+                                    error.message, error.code
+                                ),
+                            )
+                        } else if let Some(result) = response.result {
+                            (
+                                DiagnosticLevel::Ok,
+                                format!(
+                                    "{name}: ok (server {} {})",
+                                    result.server_info.name, result.server_info.version
+                                ),
+                            )
+                        } else {
+                            (
+                                DiagnosticLevel::Fail,
+                                format!("{name}: initialize returned no result"),
+                            )
+                        }
+                    }
+                    Ok(Err(error)) => (
+                        DiagnosticLevel::Fail,
+                        format!("{name}: spawn/initialize failed: {error}"),
+                    ),
+                    Err(_) => (
+                        DiagnosticLevel::Fail,
+                        format!("{name}: timed out during initialize"),
+                    ),
+                }
+            });
+            detail
+        }
+        other => (
+            DiagnosticLevel::Warn,
+            format!(
+                "{name}: transport {:?} configured (active health probe not implemented)",
+                other.transport()
+            ),
+        ),
+    }
+}
+
+fn check_mcp_server_health(config: Option<&runtime::RuntimeConfig>) -> DiagnosticCheck {
+    let Some(config) = config else {
+        return DiagnosticCheck::new(
+            "MCP server health",
+            DiagnosticLevel::Warn,
+            "runtime config could not be loaded, so MCP servers were not inspected",
+        );
+    };
+    let servers = config.mcp().servers();
+    if servers.is_empty() {
+        return DiagnosticCheck::new(
+            "MCP server health",
+            DiagnosticLevel::Warn,
+            "no MCP servers are configured",
+        );
+    }
+    let results = servers
+        .iter()
+        .map(|(name, server)| check_one_mcp_server(name, server))
+        .collect::<Vec<_>>();
+    let level = if results
+        .iter()
+        .any(|(level, _)| *level == DiagnosticLevel::Fail)
+    {
+        DiagnosticLevel::Fail
+    } else if results
+        .iter()
+        .any(|(level, _)| *level == DiagnosticLevel::Warn)
+    {
+        DiagnosticLevel::Warn
+    } else {
+        DiagnosticLevel::Ok
+    };
+    DiagnosticCheck::new(
+        "MCP server health",
+        level,
+        format!("checked {} configured MCP server(s)", servers.len()),
+    )
+    .with_details(results.into_iter().map(|(_, detail)| detail).collect())
+}
+
+fn check_network_connectivity() -> DiagnosticCheck {
+    let address = match ("api.anthropic.com", 443).to_socket_addrs() {
+        Ok(mut addrs) => match addrs.next() {
+            Some(addr) => addr,
+            None => {
+                return DiagnosticCheck::new(
+                    "Network connectivity",
+                    DiagnosticLevel::Fail,
+                    "DNS resolution returned no addresses for api.anthropic.com",
+                );
+            }
+        },
+        Err(error) => {
+            return DiagnosticCheck::new(
+                "Network connectivity",
+                DiagnosticLevel::Fail,
+                format!("failed to resolve api.anthropic.com: {error}"),
+            );
+        }
+    };
+    match TcpStream::connect_timeout(&address, Duration::from_secs(5)) {
+        Ok(stream) => {
+            let _ = stream.shutdown(std::net::Shutdown::Both);
+            DiagnosticCheck::new(
+                "Network connectivity",
+                DiagnosticLevel::Ok,
+                format!("connected to {address}"),
+            )
+        }
+        Err(error) => DiagnosticCheck::new(
+            "Network connectivity",
+            DiagnosticLevel::Fail,
+            format!("failed to connect to {address}: {error}"),
+        ),
+    }
+}
+
+fn check_system_info(cwd: &Path, config: Option<&runtime::RuntimeConfig>) -> DiagnosticCheck {
+    let mut details = vec![
+        format!("os={} arch={}", env::consts::OS, env::consts::ARCH),
+        format!("cwd={}", cwd.display()),
+        format!("cli_version={VERSION}"),
+        format!("build_target={}", BUILD_TARGET.unwrap_or("<unknown>")),
+        format!("git_sha={}", GIT_SHA.unwrap_or("<unknown>")),
+    ];
+    if let Some(config) = config {
+        details.push(format!(
+            "resolved_model={} loaded_config_files={}",
+            config.model().unwrap_or(DEFAULT_MODEL),
+            config.loaded_entries().len()
+        ));
+    }
+    DiagnosticCheck::new(
+        "System info",
+        DiagnosticLevel::Ok,
+        "captured local runtime and build metadata",
+    )
+    .with_details(details)
+}
+
 fn print_system_prompt(cwd: PathBuf, date: String) {
     match load_system_prompt(cwd, date, env::consts::OS, "unknown") {
         Ok(sections) => println!("{}", sections.join("\n\n")),
@@ -2358,6 +2984,7 @@ fn print_help() {
     println!("  rusty-claude-cli system-prompt [--cwd PATH] [--date YYYY-MM-DD]");
     println!("  rusty-claude-cli login");
     println!("  rusty-claude-cli logout");
+    println!("  rusty-claude-cli doctor");
     println!();
     println!("Flags:");
     println!("  --model MODEL              Override the active model");
@@ -2384,6 +3011,7 @@ fn print_help() {
     println!("  rusty-claude-cli --allowedTools read,glob \"summarize Cargo.toml\"");
     println!("  rusty-claude-cli --resume session.json /status /diff /export notes.txt");
     println!("  rusty-claude-cli login");
+    println!("  rusty-claude-cli doctor");
 }
 
 #[cfg(test)]
@@ -2525,7 +3153,7 @@ mod tests {
     }
 
     #[test]
-    fn parses_login_and_logout_subcommands() {
+    fn parses_login_logout_and_doctor_subcommands() {
         assert_eq!(
             parse_args(&["login".to_string()]).expect("login should parse"),
             CliAction::Login
@@ -2534,6 +3162,10 @@ mod tests {
             parse_args(&["logout".to_string()]).expect("logout should parse"),
             CliAction::Logout
         );
+        assert_eq!(
+            parse_args(&["doctor".to_string()]).expect("doctor should parse"),
+            CliAction::Doctor
+        );
     }
 
     #[test]
@@ -2797,7 +3429,7 @@ mod tests {
     fn status_context_reads_real_workspace_metadata() {
         let context = status_context(None).expect("status context should load");
         assert!(context.cwd.is_absolute());
-        assert_eq!(context.discovered_config_files, 3);
+        assert_eq!(context.discovered_config_files, 5);
         assert!(context.loaded_config_files <= context.discovered_config_files);
     }
 
@@ -2894,6 +3526,87 @@ mod tests {
         assert!(help.contains("Shift+Enter/Ctrl+J"));
     }
 
+    #[test]
+    fn oauth_status_classifies_missing_and_expired_tokens() {
+        let root = std::env::temp_dir().join(format!(
+            "doctor-oauth-status-{}",
+            std::time::SystemTime::now()
+                .duration_since(std::time::UNIX_EPOCH)
+                .expect("time")
+                .as_nanos()
+        ));
+        std::fs::create_dir_all(&root).expect("temp dir");
+        std::env::set_var("CLAUDE_CONFIG_HOME", &root);
+
+        assert_eq!(
+            super::classify_oauth_status()
+                .expect("missing should classify")
+                .0,
+            super::OAuthDiagnosticStatus::Missing
+        );
+
+        runtime::save_oauth_credentials(&runtime::OAuthTokenSet {
+            access_token: "token".to_string(),
+            refresh_token: Some("refresh".to_string()),
+            expires_at: Some(1),
+            scopes: vec!["scope:a".to_string()],
+        })
+        .expect("save oauth");
+        assert_eq!(
+            super::classify_oauth_status()
+                .expect("expired should classify")
+                .0,
+            super::OAuthDiagnosticStatus::ExpiredRefreshable
+        );
+
+        runtime::clear_oauth_credentials().expect("clear oauth");
+        std::fs::remove_dir_all(&root).expect("cleanup");
+        std::env::remove_var("CLAUDE_CONFIG_HOME");
+    }
+
+    #[test]
+    fn config_validation_flags_invalid_json() {
+        let root = std::env::temp_dir().join(format!(
+            "doctor-config-{}",
+            std::time::SystemTime::now()
+                .duration_since(std::time::UNIX_EPOCH)
+                .expect("time")
+                .as_nanos()
+        ));
+        std::fs::create_dir_all(&root).expect("temp dir");
+        let path = root.join("settings.json");
+        std::fs::write(&path, "[]").expect("write invalid top-level");
+        let check = super::validate_config_file(&path);
+        assert!(check.exists);
+        assert!(!check.valid);
+        assert!(check.note.contains("not an object"));
+        std::fs::remove_dir_all(&root).expect("cleanup");
+    }
+
+    #[test]
+    fn doctor_report_renders_requested_sections() {
+        let report = super::DoctorReport {
+            checks: vec![
+                super::DiagnosticCheck::new(
+                    "API key validity",
+                    super::DiagnosticLevel::Ok,
+                    "accepted",
+                ),
+                super::DiagnosticCheck::new(
+                    "System info",
+                    super::DiagnosticLevel::Warn,
+                    "captured",
+                )
+                .with_details(vec!["os=linux".to_string()]),
+            ],
+        };
+        let rendered = report.render();
+        assert!(rendered.contains("Doctor diagnostics"));
+        assert!(rendered.contains("API key validity"));
+        assert!(rendered.contains("System info"));
+        assert!(rendered.contains("Warnings         1"));
+    }
+
     #[test]
     fn tool_rendering_helpers_compact_output() {
         let start = format_tool_call_start("read_file", r#"{"path":"src/main.rs"}"#);