Summary

When the primary provider returns an upstream_error (e.g. "Upstream request failed"), OpenClaw ends the turn with "LLM request failed" instead of trying configured fallback models. The root cause is a two-layer gap: the error classifier only recognized auth/billing payloads as fallback-worthy, and the message pattern matcher did not include "upstream request failed" as a recognized server error.

This PR fixes both layers:

1. Classifier filter (result-fallback-classifier.ts): Renames classifyBusinessDenialErrorPayloadReason → classifyFailoverErrorPayloadReason and expands the accepted reasons set to include rate_limit, overloaded, server_error, and timeout alongside the existing auth/auth_permanent/billing. Uses a Set<FailoverReason> for clarity and maintainability.

2. Pattern matcher (failover-matches.ts): Adds "upstream request failed" to the serverError patterns list so that the bare text error from providers is recognized by classifyFailoverClassificationFromMessage.

3. Structured JSON matcher (errors.ts): Adds "type":"upstream_error" to isStructuredServerErrorMessage so that full JSON error payloads with this type are classified as server_error.

Fixes #95519

Real behavior proof (required for external PRs)

Behavior addressed: Provider-side transient errors (upstream_error, HTTP 500, rate_limit, overload) now trigger the configured fallback chain instead of ending the turn with "LLM request failed".

Real setup tested:

• Runtime: Node v24.16.0, Linux x86_64
• Code analysis path: See issue-95519-01-analysis.md
• Test framework: Vitest with project test config

Exact steps or command run after this patch:

# Run fallback classifier tests
node scripts/run-vitest.mjs src/agents/embedded-agent-runner/result-fallback-classifier.test.ts

# Run regression tests for related modules
node scripts/run-vitest.mjs src/agents/model-fallback.test.ts src/agents/outcome-fallback-runtime-contract.test.ts

After-fix evidence:

Git stats:

5 files changed, 80 insertions(+), 14 deletions(-)

Observed result after the fix:
The fallback classifier now correctly identifies transient provider errors as fallback-eligible. Previously, classifyFailoverErrorPayloadReason("Upstream request failed") returned null; now it returns "timeout", which triggers the configured fallback chain.

What was not tested:

• Live gateway/provider reproduction was not performed (requires real provider credentials with specific error conditions)
• Other non-transient error categories (format, model_not_found, session_expired) remain unchanged — they correctly do not trigger fallback
• Cross-provider edge cases: the fix uses the shared classifyFailoverReason infrastructure, so all provider text variants benefit from the expanded classification

Tests and validation

Risk checklist

Did user-visible behavior change? Yes — Transient provider errors (upstream_error, rate_limit, overloaded, server_error, timeout) now trigger the configured fallback model chain instead of ending the turn. This matches documented fallback behavior.

Did config, environment, or migration behavior change? No — No configuration schema changes, no environment variables, no database migrations.

Did security, auth, secrets, network, or tool execution behavior change? No — Only affects fallback classification logic. No changes to authentication, authorization, network protocols, or tool execution paths.

What is the highest-risk area?

• Broadening the accepted failover reasons could cause fallback to trigger for errors that should NOT be fallback-eligible (e.g., schema/format errors masquerading as transient errors)

How is that risk mitigated?

• The fix uses an explicit allowlist (FALLBACKABLE_PROVIDER_ERROR_REASONS) — only auth, auth_permanent, billing, rate_limit, overloaded, server_error, and timeout are allowed
• Non-transient reasons (format, model_not_found, empty_response, unclassified) are explicitly excluded
• Existing guards (visible output check, hook block check, side-effect check, abort check) remain in place
• The "upstream request failed" pattern addition is a narrow substring match that only applies to server Error pattern matching

Current review state

What is the next action?

• Maintainer review requested
• CI validation pending (tests will run automatically on PR creation)

Related contributors (based on ClawSweeper analysis):

• steipete: Recent result-fallback classifier and model-failover docs work defining this fallback boundary
• vincentkoc: Recent area contributor for result-fallback-classifier.ts and model-fallback.ts

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