#14395: feat: add gateway.nodes.execEvents config to control exec completion system messages

## Summary Adds a new config option `gateway.nodes.execEvents` to control how async exec completion events are surfaced in chat sessions. ### The Problem When using the `nodes` tool to run commands on remote nodes, completion results are delivered **twice**: 1. As the tool call response (used by the agent immediately) 2. As a `System: Exec finished...` system event injected into the chat session This causes duplicate context consumption — the same output (docker listings, file contents, etc.) appears multiple times in the conversation history, wasting tokens and degrading effective context window size. ### Solution New config option `gateway.nodes.execEvents` with three modes: | Mode | Behavior | |------|----------| | `inject` (default) | Current behavior — full output injected as system messages | | `notify` | Brief one-liner notification without output body | | `silent` | Suppressed entirely (heartbeat still fires) | ### Config Example ```json { "gateway": { "nodes": { "execEvents": "silent" } } } ``` ### Changes - `src/config/types.gateway.ts` — Added `execEvents` to `GatewayNodesConfig` type - `src/config/zod-schema.ts` — Added Zod validation for the new field - `src/config/schema.hints.ts` — Added UI label - `src/config/schema.field-metadata.ts` — Added label + description - `src/gateway/server-node-events.ts` — Reads config and gates system event injection ### Backward Compatible Default is `inject` which preserves existing behavior. No breaking changes. Closes #4074 <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR adds a new `gateway.nodes.execEvents` configuration option (schema + UI metadata) to control whether async node exec events are injected into chat sessions as system messages. Key changes: - Extends `GatewayNodesConfig` and config validation (`src/config/types.gateway.ts`, `src/config/zod-schema.ts`). - Adds UI labels/help text (`src/config/schema.hints.ts`, `src/config/schema.field-metadata.ts`). - Updates node event handling to conditionally enqueue system events for `exec.*` events based on the new config (`src/gateway/server-node-events.ts`). <h3>Confidence Score: 4/5</h3> - Mostly safe to merge, but clarify/fix execEvents scoping and consider avoiding per-event config loads. - The config/type/schema updates are consistent and low risk, but the event gating currently applies to exec.started/exec.denied as well as completion, which may be an unintended behavioral change relative to the stated goal. Also, calling loadConfig() on every exec event can create unnecessary overhead when the config cache expires. - src/gateway/server-node-events.ts <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} <!-- /greptile_comment -->