Problem

In the webchat chat handler, when an agent run produced only error payloads (e.g. auth failure, CLI crash) emitted as final-kind dispatcher replies, the error was silently dropped:

• the deliver collector pushed all final text into finalReplyParts without distinguishing payload.isError;
• the post-run .then() calls broadcastChatFinal only on the non-agent-run path (if (!agentRunStarted));
• broadcastChatError fired solely from .catch() (promise rejection), never for in-band error payloads.

So an error-only agent run resolved normally, marked the run ok, and surfaced nothing to the webchat UI.

Fix (src/gateway/server-methods/chat.ts)

• Collect error text in a dedicated errorReplyParts array (kept out of finalReplyParts), and set hasErrorPayload before the empty-text early return so text-less error payloads still mark the run as errored.
• In the post-run handler, when an agent run produced only error payloads (finalReplyParts empty, errorReplyParts non-empty), broadcast the combined error to the webchat UI. A mixed run (error + assistant text) is not misclassified — the assistant text still flows via the agent run's own stream.

Provenance / regression context

This fix was previously merged and then silently reverted by a later upstream sync that overwrote chat.ts (upstream never carried it). The accompanying chat.error-propagation.test.ts was left behind and had been passing vacuously — its assertions held trivially against the broken code.

Tests (chat.error-propagation.test.ts)

• New — "broadcasts error when agent run produces only error payloads": asserts exactly one error-state broadcast carrying the error text, and no final broadcast. Verified it fails on the unfixed code (1 failed / 3 passed) and passes with the fix (4/4) — a real regression guard, not vacuous.
• The 3 pre-existing assertions now hold meaningfully (mixed run → no error broadcast; empty-text error → flag set, no broadcast; non-agent run → final broadcast).

pnpm check (format + tsgo typecheck + lint + fork guards) passes.

Note: like the rest of the gateway suite, this file is gated out of the default test CI job behind REMOTECLAW_TEST_INCLUDE_GATEWAY=1 (orthogonal pre-existing failures — see the test-gateway-preauth comment in ci.yml), so the assertions run in the gateway lane / locally. Because this fix was lost once to a sync overwrite, the hardened test is the regression signal whenever the gateway suite runs.

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