fix(opencode): discard a failed attempt's output before retrying the stream

[kvnloo]

Tip leaf (fork-only) — CLEAN

Mirrors upstream origin anomalyco#51548 onto this fork for diversify evidence. Not an upstream promote.

What: Discard a failed stream attempt's output before retry so poisoned text/reasoning/tools are not retained across retries.

Branch: tip/51548-discard-failed-attempt-output
Fork commit: bafa1d4755b0
Origin tip SHA: 7d53258ff232
Tracks: issue #134

Proof (fail → pass → restore)

cd packages/opencode
bun test test/session/processor-effect.test.ts -t 'discards failed|does not retry a stream after executing|retries a pending tool|retains partial text on non-retryable|keeps parts of previously completed|retains the original snapshot|retries an empty unknown-finish|surfaces an error when an empty stream|accepts text even without a finish|accepts tool output even without'
# GREEN: 11 pass
# NEGATIVE (base product + tip tests): 8 fail / 3 pass
# RESTORE: 11 pass

github_writes_origin: 0 — fork only. Codex promote parked.

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[github-actions]

Thanks for your contribution!

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[kvnloo]

READY_UPSTREAM

Rechecked before promotion:

• upstream PR fix(opencode): discard a failed attempt's output before retrying the stream anomalyco/opencode#51548 is still open
• upstream head is exactly 7d53258ff232570b301387e62a39775504f12945
• no prior kvnloo validation comment is present
• this fork leaf's fail → pass → restore evidence therefore still applies to the exact upstream head

GitHub App cannot write to anomalyco/opencode from this environment (403). Hermes/local-gh may post the evidence comment from this fork PR. Do not open a duplicate PR.