Fixes #71620.

Root cause

@mariozechner/pi-ai providers (anthropic, google, google-vertex, openai-completions, openai-responses, mistral, amazon-bedrock, azure-openai-responses, google-gemini-cli) all throw a literal Error("An unknown error occurred") from a shared stream-wrapper pattern when the stream ends with stopReason: "aborted" | "error" and no specific error info is attached.

OpenClaw classified that bare string as transient (timeout) for failover only when the active provider name contained "anthropic", via isAnthropicGenericUnknownError() in src/agents/pi-embedded-helpers/errors.ts:756. For non-Anthropic primaries (the issue reporter is on google/gemini-2.5-flash) the classifier returned null, so:

• isFailoverAssistantError() → false
• failoverFailure branch in pi-embedded-runner/run.ts:1301 never fires
• The configured agents.defaults.model.fallbacks chain is silently bypassed
• The literal An unknown error occurred text is surfaced to end users

This is provider-agnostic upstream, but the gate was provider-scoped.

Fix

src/agents/pi-embedded-helpers/errors.ts:756: rename isAnthropicGenericUnknownError(raw, provider) to isGenericUnknownStreamError(raw) and drop the isProvider(provider, "anthropic") gate. Replace the includes("an unknown error occurred") substring check with an anchored regex /^\s*an unknown error occurred\.?\s*$/i so we only catch the bare wrapper message and not user-text or assistant prose that happens to contain the phrase.

Tests previously locked the old behavior in two places:

• pi-embedded-helpers.isbillingerrormessage.test.ts:742 — classifies provider-scoped generic upstream messages (kept the OpenRouter assertions, dropped the "An unknown error occurred" line because it no longer needs scoping)
• pi-embedded-helpers.isbillingerrormessage.test.ts:754 and failover-error.test.ts:459 — does not classify provider-scoped generic upstream messages without provider context (kept the Provider returned error / Key limit exceeded lines, dropped the "An unknown error occurred" lines that were the bug)

Added new tests covering bare/case/whitespace variants across providers anthropic, google, openrouter, plus negative tests for wrapped messages (LLM request failed with an unknown error. and a sentence containing the phrase mid-string) so they keep returning null.

Verification

• pnpm test src/agents/pi-embedded-helpers.isbillingerrormessage.test.ts src/agents/failover-error.test.ts — 189/189 passed.
• pnpm test src/plugins/provider-runtime.test.ts — 30/30 passed (uses the same classifier through isFailoverErrorMessage).
• npx oxlint <changed files> — 0 errors, 0 warnings.
• pnpm format:check <changed files> — clean.
• pnpm tsgo:core — same set of pre-existing unrelated errors as on c070509b7f (ui/src/ui/views/agents-*.ts, src/mcp/*, src/media/qr-runtime.ts, src/plugin-sdk/*, src/trajectory/metadata.ts); confirmed by stashing and re-running on clean main.

Test plan

• Existing failover regression tests pass with new behavior.
• Added regression coverage for [Bug]: Generic "An unknown error occurred" stream errors don't trigger model fallback for non-Anthropic providers #71620 across providers and case/whitespace variants.
• Negative tests prevent the substring match from accidentally classifying wrapped or descriptive prose.
• Live verification with a non-Anthropic primary that hits stopReason: "error" (issue reporter has confirmed the local one-line patch works on 2026.4.15).