feat: API timeout config, Retry-After header, configurable retry, and 400 transient retry

Cherry-picked from PR #2816 onto current upstream/main, resolving
conflicts from PR #3015's merge (which added retry_after to ApiError
but some construction sites were missing it).

Commits preserved:
- ade85398: API timeout config, Retry-After header, configurable retry
  - TimeoutConfig in HTTP client builder (connect 30s, request 5min)
  - CLAW_API_CONNECT_TIMEOUT and CLAW_API_REQUEST_TIMEOUT env vars
  - Retry-After header parsing on 429 responses
  - ApiTimeoutConfig in runtime config (settings.json)
- 8a883430: retry 400 responses with transient gateway error bodies
  - Detects known gateway phrases in 400 response bodies
  - Marks them as retryable instead of hard-failing
- ed91a61e: add 'no parseable body' to CONTEXT_WINDOW_ERROR_MARKERS
  - Some providers return 400 with 'no parseable body' for oversized
    requests instead of a proper context_length_exceeded error

Commits skipped (already in upstream via PR #3015):
- 453ab642: optional id field (already merged)
- baa8d1ba: HTML detection in streaming (already merged)
- 33d2f789: JSON error detection in streaming (already merged)

8 files changed, 299 insertions, 80 deletions

rust/crates/runtime/src/lib.rs

@@ -65,13 +65,12 @@ pub use compact::{
     get_compact_continuation_message, should_compact, CompactionConfig, CompactionResult,
 };
 pub use config::{
-    ApiTimeoutConfig, ConfigEntry, ConfigError, ConfigLoader, ConfigSource,
-    McpConfigCollection, McpManagedProxyServerConfig, McpOAuthConfig, McpRemoteServerConfig,
-    McpSdkServerConfig, McpServerConfig, McpStdioServerConfig, McpTransport,
+    suppress_config_warnings_for_json_mode, ApiTimeoutConfig, ConfigEntry, ConfigError,
+    ConfigLoader, ConfigSource, McpConfigCollection, McpManagedProxyServerConfig, McpOAuthConfig,
+    McpRemoteServerConfig, McpSdkServerConfig, McpServerConfig, McpStdioServerConfig, McpTransport,
     McpWebSocketServerConfig, OAuthConfig, ProviderFallbackConfig, ResolvedPermissionMode,
     RuntimeConfig, RuntimeFeatureConfig, RuntimeHookConfig, RuntimePermissionRuleConfig,
-    RuntimePluginConfig, ScopedMcpServerConfig, suppress_config_warnings_for_json_mode,
-    CLAW_SETTINGS_SCHEMA_NAME,
+    RuntimePluginConfig, ScopedMcpServerConfig, CLAW_SETTINGS_SCHEMA_NAME,
 };
 pub use config_validate::{
     check_unsupported_format, format_diagnostics, validate_config_file, ConfigDiagnostic,