llm_browser_testkit/

lib.rs

//! LLM-driven browser test framework.
//!
//! Provides reusable building blocks for browser-based test scenarios:
//! - Browser client via Chrome `DevTools` Protocol (headless)
//! - LLM client for natural language element targeting and assertions
//! - A2A agent integration for agent-to-agent communication
//! - MCP client/server integration for tool-calling
//! - Cost tracking, token counting, and budget enforcement
//! - Declarative TOML scenario runner
//! - `#[browser_test]` macros for `cargo test` integration

#![allow(
    clippy::expect_used,
    clippy::unwrap_used,
    clippy::panic,
    clippy::missing_panics_doc
)]

/// A2A agent protocol client.
pub mod a2a;
/// Auth token resolution — Entra ID and token commands for LLM endpoints.
mod auth;
/// AWS Bedrock provider (`SigV4`-signed Converse calls; feature `aws`).
#[cfg(feature = "aws")]
mod bedrock;
/// Budget tracking and enforcement.
pub mod budgets;
/// Cost calculation, usage tracking, and pricing.
pub mod costs;
/// Failure diagnostics — page-state capture and artifact writing.
pub mod diagnostics;
/// Endpoint registry and routing resolver.
pub mod endpoints;
/// Typed run events emitted by the runner.
pub mod events;
/// MCP client for connecting to external MCP servers.
pub mod mcp_client;
/// MCP server for exposing the framework as an MCP server.
pub mod mcp_server;
/// Concurrent execution of multiple scenario files across isolated browsers.
pub mod parallel;
/// Secret redaction for every report sink.
pub mod redact;
/// Run reporting: console, NDJSON, JUnit, GitHub and Perfetto sinks.
pub mod reporting;
/// Step-by-step scenario executor (navigate, click, type, wait, assert).
pub mod runner;
/// Declarative TOML-based test scenario types.
pub mod scenario;
/// CSS selector sanitization for LLM-generated selectors.
pub mod selectors;
/// Vision support — screenshot capture/downscale/encode for visual asserts.
pub mod vision;

/// A2A agent server for accepting agent tasks.
#[cfg(feature = "a2a-server")]
pub mod a2a_server;

/// `#[browser_test]` macros for `cargo test` integration.
#[cfg(feature = "macros")]
pub mod macros;

use std::collections::HashMap;
use std::time::Duration;

use serde_json::{json, Value};

pub use costs::LlmResponse;
pub use costs::LlmUsage;
pub use scenario::AuthConfig;
pub use scenario::AuthMode;
pub use scenario::AwsConfig;
pub use scenario::Provider;

/// Configuration for the LLM client — bundles URL, model, auth, timeouts,
/// and provider-specific options into a single struct passed everywhere.
#[derive(Debug, Clone)]
pub struct LlmConfig {
    /// OpenAI-compatible API base URL (without trailing `/v1/…`).
    pub url: String,
    /// Model name (e.g. `gpt-4o-mini`, `deepseek`).
    pub model: String,
    /// API key sent as `Authorization: Bearer <key>`.
    pub api_key: Option<String>,
    /// Custom headers appended to every LLM request.
    pub headers: HashMap<String, String>,
    /// HTTP timeout.
    pub timeout: Duration,
    /// Sampling temperature (0.0–1.0).
    pub temperature: f64,
    /// Enable extended thinking / reasoning tokens.
    /// `None` = don't send any thinking key (provider default).
    pub thinking: Option<bool>,
    /// Provider-specific parameters merged into the request body
    /// (e.g. `effort = "high"` for Anthropic).
    pub model_params: HashMap<String, Value>,
    /// How many times a single call to this endpoint is retried on
    /// transient failures before giving up (or moving to the next fallback
    /// endpoint). Default 3; override globally with
    /// `HARNESS_LLM_CALL_ATTEMPTS`.
    pub max_attempts: u32,
    /// LLM provider protocol (defaults to OpenAI-compatible).
    ///
    /// `azure` switches to the `Azure` `OpenAI` deployments endpoint, `bedrock`
    /// to the `SigV4`-signed AWS Bedrock Converse API (feature `aws`).
    pub provider: Provider,
    /// `Azure` `OpenAI` deployment name (`Provider::Azure`). Defaults to
    /// `model` when unset.
    pub deployment: Option<String>,
    /// `Azure` `OpenAI` API version (`Provider::Azure`). Defaults to
    /// `2024-10-21`.
    pub api_version: Option<String>,
    /// Authentication configuration (API key, token command, Entra ID).
    pub auth: AuthConfig,
    /// Extra HTTP headers produced by running a command per call, keyed by
    /// header name. Provider-agnostic.
    pub header_commands: HashMap<String, String>,
    /// AWS credential settings (`Provider::Bedrock`).
    pub aws: AwsConfig,
}

impl Default for LlmConfig {
    fn default() -> Self {
        Self {
            url: String::new(),
            model: String::new(),
            api_key: None,
            headers: HashMap::new(),
            timeout: Duration::from_secs(60),
            temperature: 0.0,
            thinking: None,
            model_params: HashMap::new(),
            max_attempts: default_llm_attempts(),
            provider: Provider::Openai,
            deployment: None,
            api_version: None,
            auth: AuthConfig::default(),
            header_commands: HashMap::new(),
            aws: AwsConfig::default(),
        }
    }
}

impl LlmConfig {
    /// Build a config from environment defaults, falling back to safe
    /// values when no env vars are set.
    #[must_use]
    pub fn from_env() -> Self {
        Self {
            url: llm_base_url(),
            model: llm_model(),
            api_key: std::env::var("HARNESS_LLM_API_KEY").ok(),
            headers: parse_headers_env(),
            timeout: Duration::from_secs(60),
            temperature: 0.0,
            thinking: None,
            model_params: HashMap::new(),
            max_attempts: default_llm_attempts(),
            provider: Provider::Openai,
            deployment: None,
            api_version: None,
            auth: AuthConfig::default(),
            header_commands: HashMap::new(),
            aws: AwsConfig::default(),
        }
    }
}

/// Default `Azure` `OpenAI` API version used when an endpoint does not set
/// `api_version`.
pub const DEFAULT_AZURE_API_VERSION: &str = "2024-10-21";

/// Builds the `Azure` `OpenAI` chat completions URL: the resource endpoint
/// (without `/openai`), the deployment name, and the API version.
#[must_use]
pub fn build_azure_url(base: &str, deployment: &str, api_version: &str) -> String {
    let base = base.trim_end_matches('/');
    let base = base
        .strip_suffix("/openai")
        .unwrap_or(base)
        .trim_end_matches('/');
    format!("{base}/openai/deployments/{deployment}/chat/completions?api-version={api_version}")
}

/// Reads `HARNESS_LLM_CALL_ATTEMPTS` (default 3) — how many times a single
/// chat completion is retried before the endpoint is considered failed.
#[must_use]
pub fn default_llm_attempts() -> u32 {
    std::env::var("HARNESS_LLM_CALL_ATTEMPTS")
        .ok()
        .and_then(|v| v.parse().ok())
        .filter(|n| *n >= 1)
        .unwrap_or(3)
}

/// Parses `HARNESS_LLM_HEADERS` env var (JSON object) into a header map.
///
/// Exposed for use by `endpoints.rs` and tests.
#[must_use]
pub fn parse_headers_env() -> HashMap<String, String> {
    let Ok(raw) = std::env::var("HARNESS_LLM_HEADERS") else {
        return HashMap::new();
    };
    let Ok(json) = serde_json::from_str::<Value>(&raw) else {
        return HashMap::new();
    };
    let Some(obj) = json.as_object() else {
        return HashMap::new();
    };
    obj.iter()
        .filter_map(|(k, v)| v.as_str().map(|s| (k.clone(), s.to_owned())))
        .collect()
}

/// Returns the target base URL from `HARNESS_BROWSER_BASE_URL` env,
/// defaulting to `http://localhost:4200`.
#[must_use]
pub fn base_url() -> String {
    std::env::var("HARNESS_BROWSER_BASE_URL").unwrap_or_else(|_| "http://localhost:4200".to_owned())
}

/// Returns the LLM server base URL from `HARNESS_LLM_TEST_URL` env,
/// defaulting to `http://localhost:8080`.
#[must_use]
pub fn llm_base_url() -> String {
    std::env::var("HARNESS_LLM_TEST_URL")
        .unwrap_or_else(|_| "http://localhost:8080".to_owned())
        .trim_end_matches('/')
        .to_owned()
}

/// Returns the LLM model name from `HARNESS_LLM_TEST_MODEL` env,
/// defaulting to `deepseek`.
#[must_use]
pub fn llm_model() -> String {
    std::env::var("HARNESS_LLM_TEST_MODEL").unwrap_or_else(|_| "deepseek".to_owned())
}

/// Returns whether to run the browser in headless mode from
/// `HARNESS_BROWSER_HEADLESS` env, defaulting to `true`.
#[must_use]
pub fn browser_headless() -> bool {
    std::env::var("HARNESS_BROWSER_HEADLESS")
        .map_or(true, |v| v != "0" && v.to_lowercase() != "false")
}

/// Builds a `reqwest::Client` with the given timeout.
#[must_use]
pub fn http_client(timeout: Duration) -> reqwest::Client {
    reqwest::Client::builder()
        .timeout(timeout)
        .build()
        .expect("build reqwest client")
}

/// Sends a chat completion request to the LLM.
///
/// Returns `Some(content)` on success, `None` on any error.
///
/// Prefer `llm_chat_with_usage` if you need token counting.
#[must_use]
pub async fn llm_chat(llm: &LlmConfig, system: &str, user: &str) -> Option<String> {
    llm_chat_with_usage(llm, system, user)
        .await
        .map(|r| r.content)
        .ok()
}

/// Sends a chat completion request to the LLM and returns both the content
/// and token usage from the API response.
///
/// Retries transient failures (network errors, HTTP 429/5xx, invalid
/// responses, and HTTP 200 + empty body — a gateway warm-up signature,
/// retried with a 3s backoff) up to `llm.max_attempts` times, and returns
/// the last underlying error instead of collapsing everything into a
/// generic "server down" message. The error text includes the HTTP status
/// and a truncated response-body snippet, so a gateway that answers with
/// an HTML error page is identifiable in CI logs instead of surfacing as a
/// bare JSON decode error. Deterministic client errors (401/403/404) are
/// not retried.
///
/// # Errors
///
/// Returns the last underlying error as a human-readable string when every
/// attempt fails (transport error, non-success HTTP status, response that is
/// not valid JSON, an empty HTTP 200 body, or a response missing
/// `choices[0].message.content`).
pub async fn llm_chat_with_usage(
    llm: &LlmConfig,
    system: &str,
    user: &str,
) -> Result<LlmResponse, String> {
    chat_with_retry(llm, system, user, None).await
}

/// Sends a vision-enabled chat completion request.
///
/// The user message carries the text prompt and one or more screenshots
/// (JPEG/PNG data URLs, ordered from the top of the page down) as
/// OpenAI-compatible `image_url` content parts.
///
/// Retries and error reporting behave like [`llm_chat_with_usage`].
///
/// # Errors
///
/// Returns the last underlying error as a human-readable string when every
/// attempt fails (transport error, non-success HTTP status, response that is
/// not valid JSON, or a response missing `choices[0].message.content`).
pub async fn llm_chat_vision_with_usage(
    llm: &LlmConfig,
    system: &str,
    user: &str,
    image_data_urls: Option<&[String]>,
) -> Result<LlmResponse, String> {
    chat_with_retry(llm, system, user, image_data_urls).await
}

/// Calls a chain of endpoints: the primary [`LlmConfig`] first, then each
/// fallback in order. Every endpoint gets its own `max_attempts` retry
/// budget; the first endpoint that answers wins.
///
/// Returns the response together with the index of the endpoint that
/// produced it (0 = primary, 1 = first fallback, …) so the caller can
/// attribute cost/usage to the right endpoint.
///
/// # Errors
///
/// Returns an error naming every endpoint that failed.
pub async fn llm_chat_with_usage_chain(
    primary: &LlmConfig,
    fallbacks: &[LlmConfig],
    system: &str,
    user: &str,
) -> Result<(LlmResponse, usize), String> {
    chat_chain_with_retry(primary, fallbacks, system, user, None).await
}

/// Vision variant of [`llm_chat_with_usage_chain`].
///
/// # Errors
///
/// Returns an error naming every endpoint that failed.
pub async fn llm_chat_vision_with_usage_chain(
    primary: &LlmConfig,
    fallbacks: &[LlmConfig],
    system: &str,
    user: &str,
    image_data_urls: Option<&[String]>,
) -> Result<(LlmResponse, usize), String> {
    chat_chain_with_retry(primary, fallbacks, system, user, image_data_urls).await
}

/// Shared chain loop: try each endpoint (primary then fallbacks) with its
/// own retry budget; first success wins.
async fn chat_chain_with_retry(
    primary: &LlmConfig,
    fallbacks: &[LlmConfig],
    system: &str,
    user: &str,
    image_data_urls: Option<&[String]>,
) -> Result<(LlmResponse, usize), String> {
    let mut failures: Vec<String> = Vec::new();
    for (i, llm) in std::iter::once(primary).chain(fallbacks.iter()).enumerate() {
        match chat_with_retry(llm, system, user, image_data_urls).await {
            Ok(resp) => return Ok((resp, i)),
            Err(e) => failures.push(format!("endpoint '{}' ({:?}): {e}", llm.url, llm.model)),
        }
    }
    let details = failures.iter().fold(String::new(), |mut acc, f| {
        use std::fmt::Write as _;
        let _ = writeln!(acc, "  - {f}");
        acc
    });
    Err(format!(
        "LLM call failed on all {} endpoint(s):\n{details}",
        failures.len()
    ))
}

/// Shared retry loop for text-only and vision chat completions.
async fn chat_with_retry(
    llm: &LlmConfig,
    system: &str,
    user: &str,
    image_data_urls: Option<&[String]>,
) -> Result<LlmResponse, String> {
    let client = http_client(llm.timeout);
    let mut last_err = String::from("LLM call failed");
    let mut attempts: u32 = 0;

    while attempts < llm.max_attempts {
        attempts += 1;
        match llm_chat_once(&client, llm, system, user, image_data_urls).await {
            Ok(resp) => return Ok(resp),
            Err(err) => {
                // An HTTP 200 with an empty body is a gateway warm-up
                // signature: give it a longer window to finish booting
                // instead of hammering it with short retries.
                let backoff = match &err {
                    LlmCallError::EmptyBody { .. } => Duration::from_secs(3),
                    _ => Duration::from_millis(500 * u64::from(attempts)),
                };
                last_err = err.to_string();
                if attempts >= llm.max_attempts || !err.is_retryable() {
                    break;
                }
                tokio::time::sleep(backoff).await;
            }
        }
    }

    Err(format!(
        "LLM call failed after {attempts} attempt(s) (endpoint {url}): {last_err}",
        url = llm.url
    ))
}

/// Builds the chat messages array. Text-only messages keep the plain
/// string `content` shape (maximum provider compatibility); vision calls
/// use the OpenAI-compatible content-part array with one `image_url` part
/// per screenshot (ordered from the top of the page down).
#[must_use]
fn build_messages(system: &str, user: &str, image_data_urls: Option<&[String]>) -> Value {
    let user_content = image_data_urls.map_or_else(
        || Value::String(user.to_owned()),
        |urls| {
            let mut parts = vec![json!({"type": "text", "text": user})];
            for url in urls {
                parts.push(json!({"type": "image_url", "image_url": {"url": url}}));
            }
            Value::Array(parts)
        },
    );
    json!([
        {"role": "system", "content": system},
        {"role": "user", "content": user_content}
    ])
}

/// Internal error type for a single LLM request attempt, distinguishing
/// transient failures (worth retrying) from deterministic configuration
/// errors (fail immediately).
enum LlmCallError {
    /// Transport-level failure (connect, timeout, TLS, …).
    Transport { message: String },
    /// Non-success HTTP status with a body snippet.
    Http { status: u16, body: String },
    /// Success status but the body is not valid JSON.
    InvalidJson {
        status: u16,
        detail: String,
        body: String,
    },
    /// Success status with an EMPTY body — the classic transient gateway
    /// warm-up signature (HTTP 200, zero bytes). Retried with a longer
    /// backoff than other errors.
    EmptyBody { status: u16 },
    /// Valid JSON but missing `choices[0].message.content`.
    MissingContent { json: String },
    /// Authentication failure: token command failed, Entra endpoint
    /// answered with an error, credentials missing, or an unsupported
    /// provider/feature combination.
    Auth { message: String },
}

impl std::fmt::Display for LlmCallError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::Transport { message } => write!(f, "LLM HTTP request failed: {message}"),
            Self::Http { status, body } => {
                write!(
                    f,
                    "LLM endpoint returned HTTP {status}: {}",
                    truncate(body, 300)
                )
            }
            Self::InvalidJson {
                status,
                detail,
                body,
            } => write!(
                f,
                "LLM endpoint returned HTTP {status} with non-JSON body ({detail}): {}",
                truncate(body, 300)
            ),
            Self::EmptyBody { status } => write!(
                f,
                "LLM endpoint returned HTTP {status} with an empty response (likely gateway warm-up)"
            ),
            Self::MissingContent { json } => write!(
                f,
                "LLM response missing choices[0].message.content: {}",
                truncate(json, 300)
            ),
            Self::Auth { message } => write!(f, "LLM authentication failed: {message}"),
        }
    }
}

impl LlmCallError {
    /// Whether another attempt may succeed. Network errors, rate limits,
    /// server errors, and 200-with-garbage responses can be transient on
    /// flaky gateways; auth/not-found errors are deterministic.
    #[must_use]
    fn is_retryable(&self) -> bool {
        match self {
            Self::Transport { .. }
            | Self::MissingContent { .. }
            | Self::EmptyBody { .. }
            | Self::Auth { .. } => true,
            Self::Http { status, .. } => {
                *status == 408 || *status == 429 || (500..600).contains(status)
            }
            Self::InvalidJson { status, .. } => {
                *status == 200 || *status == 408 || *status == 429 || (500..600).contains(status)
            }
        }
    }
}

/// Single LLM chat request attempt; returns the underlying error as text.
async fn llm_chat_once(
    client: &reqwest::Client,
    llm: &LlmConfig,
    system: &str,
    user: &str,
    image_data_urls: Option<&[String]>,
) -> Result<LlmResponse, LlmCallError> {
    match llm.provider {
        Provider::Openai | Provider::Azure => {
            chat_openai_compat_once(client, llm, system, user, image_data_urls).await
        }
        Provider::Bedrock => {
            #[cfg(feature = "aws")]
            let result =
                crate::bedrock::chat_once(client, llm, system, user, image_data_urls).await;
            #[cfg(not(feature = "aws"))]
            let result = Err(LlmCallError::Auth {
                message:
                    "provider = \"bedrock\" requires building llm-browser-testkit with the `aws` \
                     cargo feature"
                        .to_owned(),
            });
            result
        }
    }
}

/// Single attempt against the OpenAI-compatible path, shared by the
/// `openai` and `azure` providers (`Azure` differs only in the URL and the
/// API-key header placement).
async fn chat_openai_compat_once(
    client: &reqwest::Client,
    llm: &LlmConfig,
    system: &str,
    user: &str,
    image_data_urls: Option<&[String]>,
) -> Result<LlmResponse, LlmCallError> {
    let url = match llm.provider {
        Provider::Openai => format!("{}/v1/chat/completions", llm.url),
        Provider::Azure => {
            let deployment = llm.deployment.clone().unwrap_or_else(|| llm.model.clone());
            let api_version = llm
                .api_version
                .clone()
                .unwrap_or_else(|| DEFAULT_AZURE_API_VERSION.to_owned());
            build_azure_url(&llm.url, &deployment, &api_version)
        }
        Provider::Bedrock => unreachable!("bedrock is dispatched before this function"),
    };

    let mut headers: Vec<(String, String)> = Vec::new();
    if llm.auth.mode == AuthMode::ApiKey {
        match (&llm.auth.api_key_header, &llm.api_key) {
            // Explicit header name wins on every provider.
            (Some(header_name), Some(key)) => {
                headers.push((header_name.clone(), key.clone()));
            }
            (Some(header_name), None) => {
                return Err(LlmCallError::Auth {
                    message: format!(
                        "auth.api_key_header `{header_name}` requires endpoint api_key to be set"
                    ),
                });
            }
            // Azure classic auth: the key travels in the `api-key` header.
            (None, Some(key)) if llm.provider == Provider::Azure => {
                headers.push(("api-key".to_owned(), key.clone()));
            }
            // OpenAI-compatible convention.
            (None, Some(key)) => {
                headers.push(("Authorization".to_owned(), format!("Bearer {key}")));
            }
            (None, None) => {}
        }
    } else if let Some(bearer) = auth::resolve_bearer_token(&llm.auth, llm.api_key.as_deref())
        .await
        .map_err(|message| LlmCallError::Auth { message })?
    {
        headers.push(("Authorization".to_owned(), format!("Bearer {bearer}")));
    }
    for (name, value) in &llm.headers {
        headers.push((name.clone(), value.clone()));
    }
    for (name, command) in &llm.header_commands {
        let value = auth::run_header_command(command)
            .await
            .map_err(|e| LlmCallError::Auth {
                message: format!("header command for `{name}` failed: {e}"),
            })?;
        headers.push((name.clone(), value));
    }

    let payload = build_openai_payload(llm, system, user, image_data_urls);

    let mut req = client.post(&url).header("Content-Type", "application/json");

    for (name, value) in headers {
        req = req.header(name.as_str(), value.as_str());
    }

    let resp = req
        .json(&payload)
        .send()
        .await
        .map_err(|e| LlmCallError::Transport {
            message: e.to_string(),
        })?;
    let status = resp.status();
    let status_u16 = status.as_u16();
    let body = resp.text().await.unwrap_or_default();
    if !status.is_success() {
        return Err(LlmCallError::Http {
            status: status_u16,
            body,
        });
    }
    if body.trim().is_empty() {
        // HTTP 200 + empty body: a transient gateway hiccup (cold-start /
        // warm-up), not a client error. Retried with a longer backoff.
        return Err(LlmCallError::EmptyBody { status: status_u16 });
    }
    let json: Value = match serde_json::from_str(&body) {
        Ok(v) => v,
        Err(e) => {
            return Err(LlmCallError::InvalidJson {
                status: status_u16,
                detail: e.to_string(),
                body,
            });
        }
    };
    let usage = costs::extract_usage(&json);
    let content = json["choices"][0]["message"]["content"]
        .as_str()
        .map(String::from)
        .ok_or_else(|| LlmCallError::MissingContent {
            json: json.to_string(),
        })?;

    Ok(LlmResponse { content, usage })
}

/// Builds the OpenAI-compatible chat completions request body (shared by the
/// `openai` and `azure` providers).
#[must_use]
fn build_openai_payload(
    llm: &LlmConfig,
    system: &str,
    user: &str,
    image_data_urls: Option<&[String]>,
) -> Value {
    let mut payload = serde_json::json!({
        "model": llm.model,
        "messages": build_messages(system, user, image_data_urls),
        "max_tokens": 4096,
        "temperature": llm.temperature
    });
    if let Some(think) = llm.thinking {
        if think {
            payload["thinking"] = serde_json::json!({"type": "enabled"});
        } else {
            payload["thinking"] = serde_json::json!({"type": "disabled"});
        }
    }
    // Merge provider-specific parameters into the request body.
    if !llm.model_params.is_empty() {
        if let Value::Object(ref mut map) = payload {
            for (key, val) in &llm.model_params {
                map.insert(key.clone(), val.clone());
            }
        }
    }
    payload
}

/// JavaScript to extract interactive elements from the current page.
/// Returns a JSON array of objects with tag, selector, and label.
pub const DOM_EXTRACT_JS: &str = r#"
(() => {
  const interactive = 'a, button, input, textarea, select, [role="button"], [onclick], [tabindex], [data-testid], [aria-label]';
  const els = document.querySelectorAll(interactive);
  const info = [];
  const seen = new Set();
  els.forEach((el, i) => {
    const rect = el.getBoundingClientRect();
    if (rect.width === 0 || rect.height === 0) return;
    const tag = el.tagName.toLowerCase();
    let selector = '';
    if (el.id) selector = '#' + CSS.escape(el.id);
    else if (el.getAttribute('data-testid')) selector = '[data-testid="' + el.getAttribute('data-testid') + '"]';
    else if (el.name) selector = '[name="' + CSS.escape(el.name) + '"]';
    else if (el.className && typeof el.className === 'string') {
      const cls = el.className.trim().split(/\\s+/)[0];
      if (cls) selector = tag + '.' + CSS.escape(cls);
    }
    if (!selector) selector = tag;
    if (seen.has(selector)) return;
    seen.add(selector);

    let label = '';
    const aria = el.getAttribute('aria-label');
    if (aria) {
      label = aria;
    } else if (tag === 'input' || tag === 'textarea' || tag === 'select') {
      label = el.placeholder || el.name || el.getAttribute('aria-label') || '';
      if (el.type && !label) label = el.type;
    } else {
      label = (el.textContent || '').trim().substring(0, 80);
    }

    info.push(i + ': ' + selector + ' [' + tag + '] "' + label + '"');
  });
  return JSON.stringify(info);
})()
"#;

/// Truncates a string to the given maximum length, appending a marker with
/// the number of omitted characters if truncation occurred.
///
/// The cut point is always a UTF-8 char boundary, so multi-byte input (umlauts,
/// emoji, CJK) can never panic the caller.
#[must_use]
pub fn truncate(s: &str, max_len: usize) -> String {
    if s.len() <= max_len {
        s.to_owned()
    } else {
        let cut = floor_char_boundary(s, max_len);
        let omitted = s[cut..].chars().count();
        format!("{}...<truncated {omitted} chars>", &s[..cut])
    }
}

/// Returns the largest char boundary index in `s` that is `<= index`.
fn floor_char_boundary(s: &str, index: usize) -> usize {
    let index = index.min(s.len());
    let mut i = index;
    while i > 0 && !s.is_char_boundary(i) {
        i -= 1;
    }
    i
}

#[cfg(test)]
mod tests {
    /// Serializes env-var-mutating tests: they race when the test binary runs
    /// them in parallel, which intermittently failed CI.
    static ENV_LOCK: std::sync::Mutex<()> = std::sync::Mutex::new(());

    /// Acquires the env lock for one test.
    fn env_guard() -> std::sync::MutexGuard<'static, ()> {
        ENV_LOCK
            .lock()
            .unwrap_or_else(std::sync::PoisonError::into_inner)
    }

    use crate::costs::extract_usage;
    use crate::truncate;
    use crate::{
        default_llm_attempts, llm_base_url, llm_model, parse_headers_env, AuthConfig, AwsConfig,
        LlmConfig, Provider,
    };

    /// Starts a minimal HTTP server that answers every chat-completions
    /// request with `status`/`body`. Returns its base URL.
    fn mock_llm_server(status: u16, body: &'static str) -> String {
        use std::io::{Read, Write};
        use std::net::TcpListener;
        let listener = TcpListener::bind("127.0.0.1:0").unwrap();
        let addr = listener.local_addr().unwrap();
        std::thread::spawn(move || {
            for stream in listener.incoming() {
                let Ok(mut stream) = stream else { break };
                let mut buf = [0u8; 4096];
                let _ = stream.read(&mut buf);
                let resp = format!(
                    "HTTP/1.1 {status} {}\r\nContent-Type: application/json\r\nContent-Length: {}\r\nConnection: close\r\n\r\n{}",
                    if status == 200 { "OK" } else { "ERROR" },
                    body.len(),
                    body
                );
                let _ = stream.write_all(resp.as_bytes());
            }
        });
        format!("http://{addr}")
    }

    const PASS_BODY: &str = r#"{"choices":[{"message":{"content":"PASS"}}],"usage":{"prompt_tokens":7,"completion_tokens":2}}"#;

    fn cfg(url: &str, attempts: u32) -> LlmConfig {
        LlmConfig {
            url: url.to_owned(),
            model: "mock".to_owned(),
            api_key: None,
            headers: std::collections::HashMap::new(),
            timeout: std::time::Duration::from_secs(10),
            temperature: 0.0,
            thinking: None,
            model_params: std::collections::HashMap::new(),
            max_attempts: attempts,
            provider: Provider::Openai,
            deployment: None,
            api_version: None,
            auth: AuthConfig::default(),
            header_commands: std::collections::HashMap::new(),
            aws: AwsConfig::default(),
        }
    }

    #[tokio::test]
    async fn test_chain_primary_success_returns_index_zero() {
        let good = mock_llm_server(200, PASS_BODY);
        let (resp, idx) = crate::llm_chat_with_usage_chain(&cfg(&good, 2), &[], "s", "u")
            .await
            .expect("primary endpoint should answer");
        assert_eq!(idx, 0);
        assert_eq!(resp.content, "PASS");
        assert_eq!(resp.usage.prompt_tokens, 7);
    }

    #[tokio::test]
    async fn test_chain_falls_back_on_empty_200() {
        // Primary always returns HTTP 200 with an EMPTY body (the gateway
        // warm-up signature) — after `max_attempts` it must hand over to the
        // fallback, which answers properly.
        let broken = mock_llm_server(200, "");
        let good = mock_llm_server(200, PASS_BODY);
        let (resp, idx) =
            crate::llm_chat_with_usage_chain(&cfg(&broken, 2), &[cfg(&good, 2)], "s", "u")
                .await
                .expect("fallback endpoint should answer");
        assert_eq!(idx, 1);
        assert_eq!(resp.content, "PASS");
    }

    #[tokio::test]
    async fn test_chain_reports_all_endpoints_on_total_failure() {
        let broken1 = mock_llm_server(200, "");
        let broken2 = mock_llm_server(503, "unavailable");
        let err =
            crate::llm_chat_with_usage_chain(&cfg(&broken1, 2), &[cfg(&broken2, 2)], "s", "u")
                .await
                .expect_err("both endpoints fail");
        assert!(err.contains("all 2 endpoint(s)"), "got: {err}");
        assert!(err.contains(&broken1), "primary URL missing: {err}");
        assert!(err.contains(&broken2), "fallback URL missing: {err}");
    }

    #[test]
    fn test_default_llm_attempts_env() {
        let _env = env_guard();
        std::env::set_var("HARNESS_LLM_CALL_ATTEMPTS", "7");
        assert_eq!(default_llm_attempts(), 7);
        std::env::set_var("HARNESS_LLM_CALL_ATTEMPTS", "0");
        assert_eq!(default_llm_attempts(), 3, "0 must fall back to default");
        std::env::set_var("HARNESS_LLM_CALL_ATTEMPTS", "junk");
        assert_eq!(default_llm_attempts(), 3, "non-numeric must fall back");
        std::env::remove_var("HARNESS_LLM_CALL_ATTEMPTS");
        assert_eq!(default_llm_attempts(), 3);
    }

    #[test]
    fn test_truncate_short() {
        assert_eq!(truncate("hello", 10), "hello");
    }

    #[test]
    fn test_truncate_long() {
        let result = truncate("hello world", 5);
        assert!(result.contains("<truncated 6 chars>"));
        assert!(result.starts_with("hello"));
    }

    #[test]
    fn test_truncate_exact_length() {
        assert_eq!(truncate("abcde", 5), "abcde");
    }

    #[test]
    fn test_truncate_empty() {
        assert_eq!(truncate("", 5), "");
    }

    #[test]
    fn test_parse_headers_env_empty() {
        let _env = env_guard();
        std::env::remove_var("HARNESS_LLM_HEADERS");
        let h = parse_headers_env();
        assert!(h.is_empty());
    }

    #[test]
    fn test_parse_headers_env_valid() {
        let _env = env_guard();
        std::env::set_var("HARNESS_LLM_HEADERS", r#"{"X-Org":"acme","X-Version":"1"}"#);
        let h = parse_headers_env();
        assert_eq!(h.get("X-Org").map(String::as_str), Some("acme"));
        assert_eq!(h.get("X-Version").map(String::as_str), Some("1"));
        std::env::remove_var("HARNESS_LLM_HEADERS");
    }

    #[test]
    fn test_parse_headers_env_invalid_json() {
        let _env = env_guard();
        std::env::set_var("HARNESS_LLM_HEADERS", "not-json");
        let h = parse_headers_env();
        assert!(h.is_empty());
        std::env::remove_var("HARNESS_LLM_HEADERS");
    }

    #[test]
    fn test_llm_config_from_env_defaults() {
        let _env = env_guard();
        #[allow(clippy::float_cmp)]
        {
            let config = LlmConfig::from_env();
            assert_eq!(config.temperature, 0.0);
            assert!(config.thinking.is_none());
            assert!(config.model_params.is_empty());
        }
    }

    #[test]
    fn test_extract_usage_full() {
        let json = serde_json::json!({
            "usage": {
                "prompt_tokens": 100,
                "completion_tokens": 200,
                "total_tokens": 300
            }
        });
        let usage = extract_usage(&json);
        assert_eq!(usage.prompt_tokens, 100);
        assert_eq!(usage.completion_tokens, 200);
        assert_eq!(usage.total_tokens, 300);
    }

    #[test]
    fn test_extract_usage_empty() {
        let json = serde_json::json!({});
        let usage = extract_usage(&json);
        assert_eq!(usage.prompt_tokens, 0);
        assert_eq!(usage.completion_tokens, 0);
        assert_eq!(usage.total_tokens, 0);
    }

    #[test]
    fn test_truncate_unicode() {
        // max_len is a byte budget; the cut lands on a char boundary.
        // 'é' is 2 bytes, so index 3 captures "hé" (h=0, é=bytes 1-2)
        assert_eq!(truncate("héllo", 3), "hé...<truncated 3 chars>");
        // Length 5 captures full string (5 bytes)
        assert_eq!(truncate("hello", 5), "hello");
    }

    #[test]
    fn test_truncate_utf8_boundary_mid_char_does_not_panic() {
        // Previously: &s[..2] panicked with "not a char boundary" because the
        // cut landed inside the 2-byte 'é'. The runner hit this on real pages
        // full of umlauts/emoji — inside the diagnostics path that was
        // supposed to save the run.
        // floor_char_boundary(2) lands BEFORE 'é' (byte 1), keeping "h".
        let result = truncate("héllo", 2);
        assert_eq!(result, "h...<truncated 4 chars>");

        // 4-byte emoji: max_len=4 lands exactly on the first 🎉 boundary? No —
        // boundary 0 is the largest <= 4 only if 4 is a boundary; it is, so
        // cut=4 keeps "🎉". Check with 5 instead: cut back to 4.
        let cut_inside = truncate("🎉🎉🎉 boom", 5);
        assert_eq!(cut_inside, "🎉...<truncated 7 chars>");
        assert!(is_valid_utf8(&cut_inside), "result must stay valid UTF-8");
    }

    #[test]
    fn test_truncate_utf8_exact_omitted_count() {
        // 5 ASCII chars cut at 10 bytes → 5 omitted
        assert_eq!(truncate("abcdefghij", 5), "abcde...<truncated 5 chars>");
        // 3 multibyte chars cut at exactly their boundary → 0... but the
        // guard `len <= max_len` returns the raw string first.
        assert_eq!(truncate("ééé", 6), "ééé");
        assert_eq!(truncate("ééé", 5), "éé...<truncated 1 chars>");
    }

    fn is_valid_utf8(s: &str) -> bool {
        std::str::from_utf8(s.as_bytes()).is_ok()
    }

    #[test]
    fn test_parse_headers_env_non_object() {
        let _env = env_guard();
        std::env::set_var("HARNESS_LLM_HEADERS", "[1, 2, 3]");
        let h = parse_headers_env();
        assert!(h.is_empty());
        std::env::remove_var("HARNESS_LLM_HEADERS");
    }

    #[test]
    fn test_parse_headers_env_nested_values_filtered() {
        let _env = env_guard();
        std::env::set_var(
            "HARNESS_LLM_HEADERS",
            r#"{"str":"val","num":42,"bool":true}"#,
        );
        let h = parse_headers_env();
        assert_eq!(h.get("str").map(String::as_str), Some("val"));
        assert!(!h.contains_key("num"));
        assert!(!h.contains_key("bool"));
        std::env::remove_var("HARNESS_LLM_HEADERS");
    }

    #[test]
    fn test_llm_config_has_default_model() {
        let _env = env_guard();
        let config = LlmConfig::from_env();
        assert!(!config.model.is_empty());
    }

    #[test]
    fn test_llm_base_url_default() {
        let _env = env_guard();
        std::env::remove_var("HARNESS_LLM_TEST_URL");
        let url = llm_base_url();
        assert_eq!(url, "http://localhost:8080");
    }

    #[test]
    fn test_llm_base_url_custom() {
        let _env = env_guard();
        std::env::set_var("HARNESS_LLM_TEST_URL", "https://custom.api.com/v1");
        let url = llm_base_url();
        assert_eq!(url, "https://custom.api.com/v1");
        std::env::remove_var("HARNESS_LLM_TEST_URL");
    }

    #[test]
    fn test_llm_base_url_trailing_slash() {
        let _env = env_guard();
        std::env::set_var("HARNESS_LLM_TEST_URL", "https://api.com/");
        let url = llm_base_url();
        assert_eq!(url, "https://api.com");
        std::env::remove_var("HARNESS_LLM_TEST_URL");
    }

    #[test]
    fn test_llm_model_default() {
        let _env = env_guard();
        std::env::remove_var("HARNESS_LLM_TEST_MODEL");
        assert_eq!(llm_model(), "deepseek");
    }

    #[test]
    fn test_llm_model_custom() {
        let _env = env_guard();
        std::env::set_var("HARNESS_LLM_TEST_MODEL", "gpt-4o");
        assert_eq!(llm_model(), "gpt-4o");
        std::env::remove_var("HARNESS_LLM_TEST_MODEL");
    }

    #[test]
    fn test_extract_usage_partial() {
        let _env = env_guard();
        let json = serde_json::json!({
            "usage": {
                "prompt_tokens": 50
            }
        });
        let usage = extract_usage(&json);
        assert_eq!(usage.prompt_tokens, 50);
        assert_eq!(usage.completion_tokens, 0);
        assert_eq!(usage.total_tokens, 0);
    }

    #[test]
    fn test_browser_headless_default() {
        let _env = env_guard();
        std::env::remove_var("HARNESS_BROWSER_HEADLESS");
        assert!(crate::browser_headless());
    }
}