Description

ToolStartEvent has a speculative: bool field used by the TUI to render [spec] prefix. In PR #3640 (#3636) all production call sites correctly keep speculative: false for normal dispatch. The speculative: true path needs to be wired when the speculation engine commits a cached result via try_commit.

Scope

• File: crates/zeph-core/src/agent/tool_execution/native.rs — build_tier_call_futures (around line 2509 per critic analysis)
• Before normal dispatch, call engine.try_commit(&tool_call) — if it returns Some(result), use the cached result and emit ToolStartEvent { speculative: true, .. }
• If try_commit returns None, proceed with normal dispatch (keep speculative: false)
• The ToolStartEvent ordering concern (critic I3): suppress or defer stamp_and_send_tier_start for indices where a speculative commit fires

Acceptance

• TUI shows [spec] prefix on committed speculative tool calls
• SpeculativeMetrics.committed increments
• speculative: false path unchanged for normal dispatch

Depends on

#3636 (merged), #3641 (try_dispatch wired — needed to have results to commit)