fix(agent-runner): deliver budget/billing error turns instead of dropping them

[assapin]

Type of Change

• Feature skill
• Utility skill
• Operational/container skill
• Fix - bug fix or security fix to source code
• Simplification
• Documentation

Description

Closes #2751.

What — Budget/token-exhausted LLM turns (e.g. an Anthropic 403 billing_error, directly or via the OneCLI gateway) now reach the user instead of being silently dropped.

Why — In streaming mode the Agent SDK doesn't throw for a budget/billing error; it yields a terminal result with is_error: true and no <message> envelope. translateEvents discarded is_error, and dispatchResultText treated the unwrapped notice as scratchpad and dropped it — then the poll-loop pushed the re-wrap nudge → new turn → same error, re-hammering the gateway until idle-kill. Net: the user got silence.

How it works

• providers/claude.ts — surface is_error on the result event, and fall back to the error subtype's errors[] for the message text (error subtypes carry no result).
• poll-loop.ts — when a result has no <message> blocks and is_error, deliver the notice verbatim to the originating channel (deliverErrorResult, the same write the catch block already uses) and skip the re-wrap nudge. The happy path and the genuine wrap-mistake nudge are untouched.

How it was tested

• TDD unit tests (bun test): assert the error notice is delivered to the channel with no nudge, and that a normal unwrapped result still nudges (regression guard).
• Full suite green: container 111 pass, host 472 pass, both typechecks + prettier.
• Verified live on a real agent image + SDK with ANTHROPIC_BASE_URL pointed at a local 403 billing_error mock: the notice is delivered to the channel and the retry loop is gone.

Dependency

Requires the gateway to emit a standard Anthropic 403 so the SDK sets is_error — e.g. OneCLI returning 403 {"type":"error","error":{"type":"billing_error","message":"…"}} instead of a fabricated HTTP 200. Detailed in #2751. (Not 429 — that's retryable, the SDK auto-retries it, and the runner only logs rate-limit events → still silent.)