Module resize_coalescer 

Adaptive resize stream coalescer.

This module implements the resize coalescing behavior specified in docs/spec/resize-scheduler.md. It provides:

• Latest-wins semantics: Only the final size in a burst is rendered
• Bounded latency: Hard deadline guarantees render within max wait
• Regime awareness: Adapts behavior between steady and burst modes
• Decision logging: JSONL-compatible evidence for each decision

Usage

use ftui_runtime::resize_coalescer::{ResizeCoalescer, CoalescerConfig};

let config = CoalescerConfig::default();
let mut coalescer = ResizeCoalescer::new(config, (80, 24));

// On resize event
let action = coalescer.handle_resize(100, 40);

// On tick (called each frame)
let action = coalescer.tick();

Regime Detection

The coalescer uses a simplified regime model with two states:

• Steady: Single resize or slow sequence — prioritize responsiveness
• Burst: Rapid resize events — prioritize coalescing to reduce work

Regime transitions are detected via event rate tracking with hysteresis.

Invariants

• Latest-wins: the final resize in a burst is never dropped.
• Bounded latency: pending resizes apply within hard_deadline_ms.
• Deterministic: identical event sequences yield identical decisions.

Failure Modes

Condition	Behavior	Rationale
hard_deadline_ms = 0	Apply immediately	Avoids zero-latency stall
rate_window_size < 2	event_rate = 0	No divide-by-zero in rate
No pending size	Return None	Avoids spurious applies

Decision Rule (Explainable)

1. If time_since_render ≥ hard_deadline_ms, apply (forced).
2. If dt ≥ delay_ms, apply when in Steady (or when BOCPD is enabled). (delay_ms = steady/burst delay, or BOCPD posterior-interpolated delay when enabled.)
3. If event_rate ≥ burst_enter_rate, switch to Burst.
4. If in Burst and event_rate < burst_exit_rate for cooldown_frames, switch to Steady.
5. Otherwise, coalesce and optionally show a placeholder.

Structs

CoalescerConfig

Configuration for the resize coalescer.

CoalescerStats

Statistics about the coalescer state.

CycleTimePercentiles

Cycle time percentiles for reflow diagnostics (bd-1rz0.7).

DecisionEvidence

Evidence supporting a scheduler decision with Bayes factors.

DecisionLog

Decision log entry for observability.

DecisionSummary

Summary of decision logs.

RegimeChangeEvent

Event emitted when regime changes between Steady and Burst (bd-bksf.6 stub).

ResizeAppliedEvent

Event emitted when a resize operation is applied (bd-bksf.6 stub).

ResizeCoalescer

Adaptive resize stream coalescer.

TelemetryHooks

Telemetry hooks for observing resize coalescer events.

Enums

CoalesceAction

Action returned by the coalescer.

Regime

Detected regime for resize events.

Type Aliases

OnCoalesceDecision

Callback type for coalesce decision events.

OnRegimeChange

Callback type for regime change events.

OnResizeApplied

Callback type for resize applied events.