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/config.rs

@@ -1184,10 +1184,8 @@ fn parse_optional_api_timeout_config(root: &JsonValue) -> Result<ApiTimeoutConfi
         return Ok(ApiTimeoutConfig::default());
     };
     let context = "merged settings.apiTimeout";
-    let connect_timeout_secs = optional_u64(obj, "connectTimeout", context)?
-        .unwrap_or(30);
-    let request_timeout_secs = optional_u64(obj, "requestTimeout", context)?
-        .unwrap_or(300);
+    let connect_timeout_secs = optional_u64(obj, "connectTimeout", context)?.unwrap_or(30);
+    let request_timeout_secs = optional_u64(obj, "requestTimeout", context)?.unwrap_or(300);
     let max_retries = optional_u64(obj, "maxRetries", context)?
         .map(|v| v as u32)
         .unwrap_or(8);