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.

nix/package-context.nix

@@ -5,6 +5,7 @@
   protocol,
   plan ? null,
   contexts ? null,
+  contextData ? null,
   packageRevisionId,
 }:
 let
@@ -14,7 +15,9 @@ let
       ${pkgs.lib.escapeShellArg packageRevisionId} > "$out"
   '';
   context =
-    if contexts == null then
+    if contextData != null then
+      contextData
+    else if contexts == null then
       builtins.fromJSON (builtins.readFile projected)
     else
       (builtins.fromJSON (builtins.readFile contexts)).${packageRevisionId};