[FEATURE]: Make session processor retries configurable #48298

Feature hasn't been suggested before

• I searched existing issues for configurable session/processor retries.

Describe the enhancement

Please make the session processor retry limit configurable, including a supported value of zero.

In OpenCode 1.18.30, packages/opencode/src/session/retry.ts fixes RETRY_MAX_RETRIES at 5. This retry layer is independent of setting provider/AI SDK retries to zero. For coding-agent workloads, a turn may have side effects, so an implicit processor replay after a transport failure can duplicate provider requests and makes strict no-replay operation impossible.

A config option or environment variable would be sufficient. The current default can remain unchanged for compatibility, while operators that require at-most-one provider attempt can select zero. Exposing the current attempt in structured diagnostics would also help clients distinguish the original failure from retry exhaustion.

Tested with OpenCode 1.18.30 on Linux x86_64 using an OpenAI-compatible provider and injected retryable transport failures.