feat(grid-agent): add generic LLM tool loop (#119)

docs/grid-agent-architecture.md

@@ -24,6 +24,8 @@ handles, the control sender, and observable receiver.
 | Coordinator task | `ServiceHandle.tasks[1]` | exactly one | shared cancellation token, joined second |
 | Body / message | typed boundary owners | 8 MiB / 64 KiB hard ceilings, with lower configured limits | rejected before enqueue |
 | Conversation / tool calls | request owner | 256 messages / 64 calls, with lower configured limits | rejected before request |
+| LLM request slots | shared `LlmClient` semaphore | 256 hard / configured concurrent requests | async acquire or cancellation |
+| Reasoning/tool session | `ToolLoop` caller | 32 turns / 256 calls hard, with lower configured limits | total timeout, cancellation, or supersession |
 | Authorized avatars | immutable `AgentConfig` set | 1,024 hard ceiling, lower configured limit | malformed, nil, duplicate, and wildcard input rejected |
 | Configuration / secret file | loader | 64 KiB / 16 KiB | regular non-symlink file only |
 
@@ -65,6 +67,10 @@ shutdown.
 - World changes cross only `WorldMutator::apply`, which always receives the
   proposed call and an explicit `PolicyDecision`. This issue supplies no live
   mutation implementation.
+- LLM traffic crosses one exact configured URL through `LlmClient`. Redirects
+  are refused, response bodies are bounded while streaming, bearer secrets are
+  redacted, and provider/model discovery does not exist. Proposed calls cross
+  `ToolExecutor` only after registered-name and schema validation.
 - Signals and console output belong to the binary. The reusable core relies on
   no terminal, Unix socket, Unix signal, separator, or fixed platform path.
 
@@ -80,8 +86,14 @@ AgentService -> bounded Tokio channels/tasks -> injected GridBackend
 typed config/events/policy boundaries    live-grid feature boundary
      |                                           |
      +-----------------> libremetaverse-types    +--> libremetaverse::GridClient
+
+avatar session -> bounded ToolLoop -> exact-endpoint LlmClient
+                       |
+                       +-> validated ToolExecutor boundary
 ```
 
 The package has no build script or direct native dependency. The focused
 `dependency_policy` test rejects subprocess launch sites, unsafe/native ABI
 source, build scripts, and unreviewed direct dependency names in this package.
+The precise LLM compatibility and cancellation contract is documented in
+[`grid-agent-llm.md`](grid-agent-llm.md).