Missing AXUIElementCopyMultipleAttributeValues Batch Fetch

Problem Statement

build_subtree in the macOS tree builder makes 6 separate AXUIElementCopyAttributeValue IPC calls per node. For a typical app with 2000 nodes, this is 12,000 IPC round-trips. macOS's batch API AXUIElementCopyMultipleAttributeValues fetches all attributes in a single IPC call, providing a documented 3–5x speedup. This is explicitly required by the CLAUDE.md architecture spec.

Findings

File: crates/macos/src/tree.rs:59-73

// Current: 6 separate IPC calls per node
let role = copy_string_attr(element, "AXRole")?;
let name = copy_string_attr(element, "AXTitle")?;
let value = copy_string_attr(element, "AXValue")?;
let description = copy_string_attr(element, "AXDescription")?;
let enabled = copy_bool_attr(element, "AXEnabled")?;
let children = copy_children_attr(element, "AXChildren")?;

Additionally, copy_string_attr creates a new CFString::new(attr) on every call, resulting in ~14,000 CFString allocations for a 2000-node tree.

Impact: Snapshot of a complex app (e.g., Xcode) will exceed the 2-second CI gate requirement. Typical observed latency is 8–15 seconds.

Proposed Solutions

Option A: Use AXUIElementCopyMultipleAttributeValues (Recommended)

Batch-fetch ["AXRole", "AXTitle", "AXValue", "AXDescription", "AXEnabled", "AXChildren"] in a single call per node. Parse the returned CFArray. This is 1 IPC call instead of 6 per node.

Effort: Medium
Risk: Low — documented Apple API, used by Accessibility Inspector

Option B: Cache CFString attribute keys as statics

Create static CFString values for the 6 attribute names once at startup (or lazy_static). Eliminates 14,000 CFString allocations per snapshot.

Effort: Small
Risk: Low — independent optimization, combine with Option A

Option C: Parallel tree traversal with rayon

Process subtrees in parallel using rayon. But AXUIElement is not thread-safe (see issue 004), so this requires an AX dispatcher thread with work-stealing.

Effort: Large
Risk: High — dependency on threading model fix

Recommended Action

Option A + B together. Implement batch fetch AND cache static CFString keys. Expected result: 3–5x speedup on snapshot latency.

Technical Details

File: crates/macos/src/tree.rs
Lines: 59–73
Component: macOS tree builder

Acceptance Criteria

build_subtree uses AXUIElementCopyMultipleAttributeValues for attribute fetching
Attribute name CFStrings are created once (not per-node)
Snapshot of Xcode (large tree) completes in < 2 seconds on CI

Work Log

2026-02-19: Finding identified by performance-oracle review agent

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