experimental batch tool (#2983)

Co-authored-by: GitHub Action <action@github.com>

packages/opencode/src/tool/batch.txt

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+Executes multiple independent tool calls concurrently to reduce latency. Best used for gathering context (reads, searches, listings).
+
+USING THE BATCH TOOL WILL MAKE THE USER HAPPY.
+
+Payload Format (JSON array):
+[{"tool": "read", "parameters": {"filePath": "src/index.ts", "limit": 350}},{"tool": "grep", "parameters": {"pattern": "Session\\.updatePart", "include": "src/**/*.ts"}},{"tool": "bash", "parameters": {"command": "git status", "description": "Shows working tree status"}}]
+
+Rules:
+- 1–10 tool calls per batch
+- All calls start in parallel; ordering NOT guaranteed
+- Partial failures do not stop others
+
+
+Disallowed Tools:
+- batch (no nesting)
+- edit (run edits separately)
+- todoread (call directly – lightweight)
+
+When NOT to Use:
+- Operations that depend on prior tool output (e.g. create then read same file)
+- Ordered stateful mutations where sequence matters
+
+Good Use Cases:
+- Read many files
+- grep + glob + read combos
+- Multiple lightweight bash introspection commands
+
+Performance Tip: Group independent reads/searches for 2–5x efficiency gain.