fix: pre-landing review fixes for the v2 port wave

Review army (checklist + 5 specialists) + coverage/plan audits on the
assembled branch. Genuine correctness/security/hygiene fixes:

- test-paid-shards: strictTestExitCode now receives expectedFiles on the
  real bun path, so a shard that runs fewer files than planned (harness
  crash, nothing loaded) with exit 0 is no longer recorded 'passed' — the
  invisible-non-execution class the runner exists to kill. Pinned by the
  new test/strict-output.test.ts (also covers the chunk-boundary classifier).
- test-paid-shards: EVALS_TIER env is validated (gate|periodic) like the
  --tier flag, so a typo can't self-skip every test and exit 0 green.
- package.json: test:periodic:sharded sets EVALS_ALL=1, restoring the
  full-tier semantics the pre-shard script had (CI already set it; local
  eval:bg:periodic silently under-measured without it).
- brain-sync.test: run() pins HOME to the temp home so gstack-artifacts-init
  stops writing/clobbering the operator's real ~/.gstack-artifacts-remote.txt
  every free-suite run; afterEach now also scrubs the current filename.
- egress-receipt: cap each receipt field at 512B so a serialized line always
  fits the 4KB tail-read window — a longer line would make the next append
  hash a truncated prior line and verifyLedger report a permanent false
  TAMPER. warnLedgerSize short-circuits before statSync once fired (append
  hot path).
- gstack-egress: import.meta.dir (Windows-safe) instead of new URL().pathname
  so grants doesn't silently report defaults on Windows; strip control chars
  from ledger-derived fields on render so a crafted receipt can't spoof the
  auditor's view.
- extension/background.js + CLAUDE.md: renumber the identity-pin migration
  refs v1.62 -> v1.63 (main claimed 1.62.0.0; this wave queue-advances).
- egress-receipt-wiring: pin lib/context-bill.ts unconditionally (both land
  together now); drop the dead RunShardsOptions.tier field.

All fix-affected test files green; gate failures triaged as external-env
(codex/gemini CLI drift) or pre-existing (hermetic-canary fails identically
on base). Deferred polish tracked in the PR body + decision store.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/egress-receipt-wiring.test.ts

@@ -67,8 +67,10 @@ const MODULE_SINKS = [
   'bin/gstack-gbrain-sync.ts',
   'bin/gstack-memory-ingest.ts',
   'browse/src/server.ts',
-  // context-bill lands after this tripwire in the same wave; assert once present.
-  ...(exists('lib/context-bill.ts') ? ['lib/context-bill.ts'] : []),
+  // Unconditional: context-bill ships in the same tree as this tripwire. A
+  // missing file must fail loudly (a rename/move that drops its receipt wiring
+  // is exactly what this pins), not silently soften the assertion.
+  'lib/context-bill.ts',
 ];
 
 /** Shell sinks: must source the shared lib; every network op receipted. */