Port bug fixes and features from Python SDK

[Savid]

Summary

Syncs the Go SDK with upstream changes from the Python Claude Agent SDK since commit 4e8e7c9fde85d92a53d7a7ca890cd0131c3f754a (38 commits, filtering to 6 meaningful changes).

Bug Fixes

• Fix thinking flag CLI args (python#796) — ThinkingConfigAdaptive and ThinkingConfigDisabled were incorrectly mapped to --max-thinking-tokens 32000 / --max-thinking-tokens 0. The CLI (v2.1.96+) now expects --thinking adaptive and --thinking disabled. Only ThinkingConfigEnabled (with explicit budget) still uses --max-thinking-tokens.

• Fix --setting-sources passed when empty (python#778) — When SettingSources was nil or empty, the SDK passed --setting-sources "" to the CLI, which caused the CLI's arg parser to consume the next flag as the value. Now only emits the flag when len > 0, consistent with AllowedTools, DisallowedTools, and Betas.

Features

• ExcludeDynamicSections in SystemPromptPreset (python#797) — When true, the CLI strips per-user dynamic sections (working directory, auto-memory, git status) from the system prompt so it's byte-identical across users, enabling cross-user prompt caching. Sent as excludeDynamicSections in the initialize control request. New WithExcludeDynamicSections(bool) option.

• WithSessionID option (python#750) — Adds SessionID field mapped to --session-id CLI flag, allowing users to specify a custom session ID (distinct from --resume which resumes an existing session).

• ToolUseID in PermissionContext (python#754) — Exposes the tool_use_id field (already sent by the CLI and extracted for deduplication) in the PermissionContext passed to CanUseTool callbacks. Enables permission logic based on specific tool call IDs.

• MCP maxResultSizeChars via _meta (python#756) — SDK MCP tools can now declare WithMaxResultSizeChars(n) to override the CLI's default 50K character hard limit for tool output. The value is forwarded as _meta: {"anthropic/maxResultSizeChars": n} in tools/list responses.

Already present in Go SDK (no changes needed)

These Python SDK additions were already implemented in the Go SDK:

• "auto" PermissionMode
• AgentDefinition background/effort/permissionMode fields
• control_cancel_request handling
• get_context_usage() / GetContextUsage()

Not applicable

• Python Annotated type for per-parameter @tool descriptions (Python-specific)
• String prompt in connect() fix (Go SDK already handles this correctly)

Files changed (15)

File	Change
internal/cli/command.go	Thinking flags, session-id flag, setting-sources guard
internal/cli/command_test.go	New tests for all CLI flag changes
internal/cli/cli_test.go	Updated existing thinking config tests
internal/config/options.go	SessionID field, updated doc comment
internal/config/preset.go	ExcludeDynamicSections field on SystemPromptPreset
internal/protocol/session.go	excludeDynamicSections in initialize payload, ToolUseID in parsePermissionContext
internal/protocol/session_test.go	Extended permission context metadata test
internal/permission/permission.go	ToolUseID field on Context
internal/mcp/sdk_server.go	AddToolWithOptions, _meta in ListTools
internal/mcp/sdk_server_test.go	Tests for maxResultSizeChars in ListTools
options.go	WithSessionID, WithExcludeDynamicSections options
sdk_mcp_tool.go	MaxResultSizeChars field, WithMaxResultSizeChars option
sdk_mcp_tool_test.go	Tests for maxResultSizeChars option and server integration
sdk_mcp_server.go	Pass MaxResultSizeChars through to internal server
examples/extended_thinking/main.go	Updated comment

Test plan

• go test -race ./... — all tests pass
• golangci-lint run --new-from-rev=origin/master — 0 issues
• New tests for thinking config (table-driven, 3 modes + negative)
• New tests for setting-sources empty/non-empty
• New tests for session-id flag
• Extended existing permission context metadata test for ToolUseID
• New tests for maxResultSizeChars (internal + public + integration)

🤖 Generated with Claude Code