Prevent worker prompts from outrunning boot readiness

Add a foundational worker_boot control plane and tool surface for
reliable startup. The new registry tracks trust gates, ready-for-prompt
handshakes, prompt delivery attempts, and shell misdelivery recovery so
callers can coordinate worker boot above raw terminal transport.

Constraint: Current main has no tmux-backed worker control API to extend directly
Constraint: First slice must stay deterministic and fully testable in-process
Rejected: Wire the first implementation straight to tmux panes | would couple transport details to unfinished state semantics
Rejected: Ship parser helpers without control tools | would not enforce the ready-before-prompt contract end to end
Confidence: high
Scope-risk: moderate
Reversibility: clean
Directive: Treat WorkerObserve heuristics as a temporary transport adapter and replace them with typed runtime events before widening automation policy
Tested: cargo test -p runtime worker_boot
Tested: cargo test -p tools worker_tools
Tested: cargo check -p runtime -p tools
Not-tested: Real tmux/TTY trust prompts and live worker boot on an actual coding session
Not-tested: Full cargo clippy -p runtime -p tools --all-targets -- -D warnings (fails on pre-existing warnings outside this slice)

rust/crates/runtime/src/lib.rs

@@ -23,6 +23,7 @@ mod sse;
 pub mod task_registry;
 pub mod team_cron_registry;
 mod usage;
+pub mod worker_boot;
 
 pub use bash::{execute_bash, BashCommandInput, BashCommandOutput};
 pub use bootstrap::{BootstrapPhase, BootstrapPlan};
@@ -99,6 +100,10 @@ pub use session::{
     SessionFork,
 };
 pub use sse::{IncrementalSseParser, SseEvent};
+pub use worker_boot::{
+    Worker, WorkerEvent, WorkerEventKind, WorkerFailure, WorkerFailureKind, WorkerReadySnapshot,
+    WorkerRegistry, WorkerStatus,
+};
 pub use usage::{
     format_usd, pricing_for_model, ModelPricing, TokenUsage, UsageCostEstimate, UsageTracker,
 };