Instrument and improve incremental workspace checks

Profile source capture, Nix evaluation/realization, resource/query checking,
and implementation builds without putting timings into immutable outputs.
Keep modular repositories; bound independent capture work, snapshot jj once
per observation, and retain final concurrent-edit and Git completeness checks.

Compose exact resource/closure/frontend/toolchain checks as memoized Nix
derivations. Preserve whole-workspace validation and the full compiler path
when no checked dependency is supplied. Share canonical Nixpkgs by content,
index workspace build contexts once, and narrow lock/driver/compiler inputs
with conservative complete-source fallback. Batch React witness checks only
when distinct source closures cannot share ambient declarations; otherwise
run the original independent TypeScript checks.

Seed local authoring toolchains with exact canonical fetch identities when
they match the selected inputs; retain store-path inputs for overrides.
Add generic correctness checks rather than permanent Reader timing/content
fixtures. Verify actual Reader edits and rejection/recovery in a private
workbench, preserving the original user's workbench and runtime.

Query checking currently caches at resource/closure boundaries, not individual
query semantic dependency boundaries. Template helper pins and reproducible
fixture snapshots follow in a separate publication change.

src/capability-language/profile.ts

@@ -0,0 +1,5 @@
+/** Observations belong in logs, never in content-addressed compiler outputs. */
+export const profile = (phase: string, started: number, details: Record<string, unknown> = {}) => {
+  if (process.env.QUIXOS_TRACE_PROFILE === "1")
+    console.error(`[qx-profile] ${JSON.stringify({ phase, ms: Math.round(performance.now() - started), ...details })}`);
+};