fix: report line-only coverage honestly and tighten Bun test helpers

The generated HTML and Cobertura reports no longer show unmeasured
branch and function coverage as 100%. Poll and waitFor deadlines use
performance.now so frozen dates cannot make them loop forever, the
malformed-configuration test covers undefined again next to the empty
array, compose health checks honor PORT, and the migration spec lists
only what is still open.

Refs #291, #292, #293

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/coverage-reports.mjs

@@ -1,7 +1,8 @@
 // Converts coverage/lcov.info (Bun) to HTML and Cobertura. Run: bun scripts/coverage-reports.mjs
 // shortcut: line coverage only, Bun's lcov has no usable branch/function data; revisit if Bun adds it.
-import { readFileSync } from 'node:fs';
-import { resolve } from 'node:path';
+// Totals here sum lines (8351/8578); Bun's text table averages per-file percentages, so it reads lower.
+import { readdirSync, readFileSync, writeFileSync } from 'node:fs';
+import { join, resolve } from 'node:path';
 import libCoverage from 'istanbul-lib-coverage';
 import libReport from 'istanbul-lib-report';
 import reports from 'istanbul-reports';
@@ -29,3 +30,26 @@ for (const record of readFileSync('coverage/lcov.info', 'utf8').split('end_of_re
 }
 const context = libReport.createContext({ dir: 'coverage', coverageMap: map });
 for (const name of ['html', 'cobertura']) reports.create(name).execute(context);
+
+// Istanbul reports 0 branches/functions as 100%; relabel them instead of claiming coverage.
+const rewrite = (file, edit) => writeFileSync(file, edit(readFileSync(file, 'utf8')));
+for (const page of readdirSync('coverage', { recursive: true }).filter((f) => f.endsWith('.html')))
+	rewrite(join('coverage', page), (html) =>
+		html
+			.replace(
+				/<span class="strong">100% <\/span>(\s*<span class="quiet">(?:Branches|Functions)<\/span>\s*<span class='fraction'>)0\/0</g,
+				'<span class="strong">n/a </span>$1not collected<',
+			)
+			.replace(
+				/<td data-value="100" class="pct \w+">100%<\/td>(\s*)<td data-value="0" class="abs \w+">0\/0<\/td>/g,
+				'<td data-value="0" class="pct">n/a</td>$1<td data-value="0" class="abs">not collected</td>',
+			),
+	);
+rewrite('coverage/cobertura-coverage.xml', (xml) =>
+	xml
+		.replaceAll('branch-rate="1"', 'branch-rate="0"')
+		.replace(
+			'<coverage ',
+			'<!-- Line coverage only: bun test does not collect branch or function coverage. -->\n<coverage ',
+		),
+);