docs(core): say 'declares the same measure', not 'the contract this result implements'

Measured: `packages/core` neither imports nor references
`packages/spec/src/kernel/startup-orchestrator.zod.ts`, and nothing in the repo
implements `IStartupOrchestrator`. The two `PluginStartupResult` declarations
describe the same domain result and share no shape, so 'implements' overstated a
relationship that does not exist in code. The reason to take the contract's name
is unchanged: it is the name the spec surface declares for this measure.

Filed separately as the wider question this made visible.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ARYe3yQTQCUFm5qPYNgKaJ

Author: claude[bot]

.changeset/core-plugin-startup-duration-name.md

@@ -6,7 +6,7 @@ Plugin startup elapsed time is now reported as `duration` — the name the spec
 
 `PluginStartupResult.startTime` (`packages/core/src/plugin-loader.ts`) has always been assigned `Date.now() - startTime`, an elapsed duration, on both the success and the failure path. The name therefore asserts the opposite of the value: a reader who correctly takes `startTime` for an instant and writes `Date.now() - result.startTime` gets an age near the epoch rather than a wait. That is the one failure mode a unit convention cannot rescue — an ambiguous name makes someone stop and check, this one lets them proceed confidently wrong.
 
-This is not a naming preference but a divergence between what is declared and what is enforced. `packages/spec/src/kernel/startup-orchestrator.zod.ts` declares `duration: z.number().min(0)` — "Time taken to start the plugin in milliseconds" — for the very result this interface implements, so the contract was already correct and `packages/core` had drifted away from it. The right spelling is also twelve lines above the defect in the same file: `PluginLoadResult.loadTime` carries the identical `Date.now() - startTime` computation under a name that does not lie.
+This is not a naming preference but a divergence between what is declared and what is enforced. `packages/spec/src/kernel/startup-orchestrator.zod.ts` declares `duration: z.number().min(0)` — "Time taken to start the plugin in milliseconds" — for the same measure on the same result, the outcome of starting one plugin. The contract surface was already correct and `packages/core` had drifted away from it. The right spelling is also twelve lines above the defect in the same file: `PluginLoadResult.loadTime` carries the identical `Date.now() - startTime` computation under a name that does not lie.
 
 Three sites move, and every one of them is additive — nothing is removed, so no consumer has to change anything on this release:
 

packages/core/src/plugin-loader.ts

@@ -94,8 +94,8 @@ export interface PluginStartupResult {
     /**
      * Elapsed milliseconds the plugin's `start()` took.
      *
-     * Named for the member the spec contract this result implements already
-     * declares -- `PluginStartupResultSchema.duration` in
+     * Named for the member `packages/spec` already declares for the same
+     * measure -- `PluginStartupResultSchema.duration` in
      * `packages/spec/src/kernel/startup-orchestrator.zod.ts` ("Time taken to
      * start the plugin in milliseconds") -- and matching `PluginLoadResult.loadTime`
      * above: the same `Date.now() - startTime` computation under a name that