feat(plugin-sdk): add resolve_exec_env hook

Summary:
- Add the plugin SDK `resolve_exec_env` hook for bounded exec environment contributions.
- Wire resolved exec env through exec preparation/final execution without exposing plugin env values to generic tool hooks.
- Cover lazy exec loading, host and command rewrites, node/gateway execution, filtering, and EXEC shell snapshot cache behavior.

Verification:
- `pnpm changed:lanes --json`
- `node scripts/run-vitest.mjs src/agents/bash-tools.exec.resolve-env-hook.test.ts src/agents/agent-tool-definition-adapter.test.ts src/agents/agent-tool-definition-adapter.after-tool-call.test.ts src/agents/shell-snapshot.test.ts src/plugins/hook-resolve-exec-env.test.ts`
- `pnpm check:test-types`
- `pnpm lint src/agents/bash-tools.exec.ts src/agents/bash-tools.exec.resolve-env-hook.test.ts`
- `.agents/skills/autoreview/scripts/autoreview --mode branch --base origin/main`
- PR CI clean on 1bbad8d071: https://github.com/openclaw/openclaw/actions/runs/26817910293

Co-authored-by: Lanzhi <lizhan3@xiaomi.com>

docs/plugins/hooks.md

@@ -120,6 +120,7 @@ observation-only.
 
 - **`before_tool_call`** - rewrite tool params, block execution, or require approval
 - `after_tool_call` - observe tool results, errors, and duration
+- `resolve_exec_env` - contribute plugin-owned environment variables to `exec`
 - **`tool_result_persist`** - rewrite the assistant message produced from a tool result
 - **`before_message_write`** - inspect or block an in-progress message write (rare)
 
@@ -233,6 +234,28 @@ for host-trusted gates such as workspace policy, budget enforcement, or
 reserved workflow safety. External plugins should use normal `before_tool_call`
 hooks.
 
+### Exec environment hook
+
+`resolve_exec_env` lets plugins contribute environment variables to `exec`
+tool invocations after the base exec environment is built and before the
+command runs. It receives:
+
+- `event.sessionKey`
+- `event.toolName`, currently always `"exec"`
+- `event.host`, one of `"gateway"`, `"sandbox"`, or `"node"`
+- context fields such as `ctx.agentId`, `ctx.sessionKey`,
+  `ctx.messageProvider`, and `ctx.channelId`
+
+Return a `Record<string, string>` to merge into the exec environment. Handlers
+run in priority order, and later hook results override earlier hook results for
+the same key.
+
+Hook output is filtered through the host exec environment key policy before it
+is merged. Invalid keys, `PATH`, and dangerous host override keys such as
+`LD_*`, `DYLD_*`, `NODE_OPTIONS`, proxy variables, and TLS override variables
+are dropped. The filtered plugin env is included in gateway approval/audit
+metadata and forwarded to node-host execution requests.
+
 ### Tool result persistence
 
 Tool results can include structured `details` for UI rendering, diagnostics,