fix(telemetry): stamp a compaction on entering the null window

Claude Code's tracker nulls recache_tokens_if_cold at a compaction or a tool-result clearing and only counts the expected rebuild at the next request, which also closes the window, so no report carried both and the old rule never fired. Stamp on the first warm null report after one that carried a value, carry it through idle re-reports and drop it at the next request; the readout now says "Context compacted at HH:MM" since a clearing opens the same window.

Also persist a changed report so a crash restores the latest one, rename the session field to statusLineExporter (statusLineTelemetry is the registry capability) and document its values, word the stake as re-cached, move the readout block above the SSE staleness heading, and drop keep-warm mentions until it lands.

src/mux-interface.ts

@@ -25,7 +25,7 @@ import type {
   SessionRemote,
   SessionDocker,
   PaneExit,
-  StatusLineTelemetry,
+  StatusLineExporter,
 } from './types.js';
 
 /**
@@ -59,7 +59,7 @@ export interface MuxSession {
   /** Whether Ralph / Todo tracking is enabled */
   ralphEnabled?: boolean;
   /** Whether the current launch carries the statusLine exporter; set on every create and respawn. */
-  statusLine?: StatusLineTelemetry;
+  statusLine?: StatusLineExporter;
   /**
    * This record was rebuilt from the tmux socket rather than from Codeman's own
    * bookkeeping, so everything on it but the name and the pid is a guess. Its