fix: opencode compat tool call rendering and default to no-token

- Fix tool name lost on ToolResult events (persist via tool_name_by_call)
- Fix tool input lost on ToolResult events (persist via tool_args_by_call)
- Fix tool output in wrong field (error -> output)
- Fix text doubling in streaming (defer emit to ItemCompleted)
- Fix missing delta field in text streaming events
- Default server mode to no-token when --token not specified
- Add install-fast-sa and install-fast-gigacode justfile targets

research/opencode-compat/COMPARISON.md

@@ -0,0 +1,70 @@
+# Native OpenCode vs Sandbox-Agent: OpenCode API Comparison
+
+## Overview
+
+Captured API output from both native OpenCode server (v1.1.49) and sandbox-agent's
+OpenCode compatibility layer, sending identical request patterns:
+1. Message 1: Simple text response (echo/text)
+2. Message 2: Tool call (ls/mock.search)
+
+## Bugs Found and Fixed
+
+### 1. Tool name (`tool` field) changed between events [FIXED]
+
+**Bug**: The `tool` field in tool part events changed between `pending` and `running`/`completed`
+states. In the `pending` event it correctly showed `"mock.search"`, but in subsequent events
+(from ToolResult) it showed `"tool"` because `extract_tool_content` doesn't return tool_name
+for ToolResult items.
+
+**Fix**: Added `tool_name_by_call` HashMap to `OpenCodeSessionRuntime` to persist tool names
+from ToolCall events and look them up during ToolResult processing.
+
+### 2. Tool `input` lost on ToolResult events [FIXED]
+
+**Bug**: When the ToolResult event came in, the tool's input arguments were lost because
+ToolResult content only contains `call_id` and `output`, not arguments.
+
+**Fix**: Added `tool_args_by_call` HashMap to `OpenCodeSessionRuntime` to persist arguments
+from ToolCall events and look them up during ToolResult processing.
+
+### 3. Tool `output` in wrong field (`error` instead of `output`) [FIXED]
+
+**Bug**: When tool result status was `Failed`, the output text was put in `"error"` field.
+Native OpenCode uses `"output"` field for tool output regardless of success/failure.
+
+**Fix**: Changed the failed tool result JSON to use `"output"` instead of `"error"`.
+
+### 4. Text doubling in streaming [FIXED]
+
+**Bug**: During text streaming, `ItemStarted` emitted a text part with full content, then
+`ItemDelta` appended delta text, then `ItemCompleted` emitted again, causing doubled text.
+
+**Fix**: `ItemStarted` now only initializes empty text in runtime without emitting a part event.
+`ItemCompleted` emits the final text using accumulated delta text or fallback to content text.
+
+### 5. Missing `delta` field in text streaming events [FIXED]
+
+**Bug**: `delta` field was not included in `message.part.updated` events for text streaming.
+Native OpenCode includes `delta` on streaming events and omits it on the final event.
+
+**Fix**: Changed `apply_item_delta` to use `part_event_with_delta` instead of `part_event`.
+
+### 6. Not bugs (noted for completeness)
+
+- **Missing `step-start`/`step-finish` parts**: These are OpenCode-specific (git snapshot
+  tracking) and not expected from sandbox-agent.
+- **Missing `time` on text parts**: Minor; could be added in future.
+- **Missing `time.completed` on some assistant messages**: Minor timing issue.
+
+## Verification
+
+After fixes, all tool events now correctly show:
+- `"tool": "mock.search"` across all states (pending, running, error)
+- `"input": {"query": "example"}` preserved across all states
+- `"output": "mock search results"` on the error event (not `"error"`)
+- Text streaming includes `delta` field
+- No text doubling
+
+All 28 OpenCode compat tests pass.
+All 10 session snapshot tests pass.
+All 3 HTTP endpoint tests pass.