Make workspace authoring converge through immutable Nix candidates

Coordinate registered resource edits bottom-up into retained exact remote sources.
Use one Nix-owned source graph for provisional checking, template publication,
explicit baseline upgrades and host activation; retain independent runtime pins.

Add scoped contract inspection, historical recovery, derived worklists, crash-safe
locks, named dependency adoption and plain-QX structural editing. Repair TODO
ownership and template instantiation, and document the supported agent workflow.

Validated with protocol and command suites, real jj/Nix convergence and cache
checks, TS/React installed-command acceptance, and fresh TODO first-edit acceptance.
No live deployment or public publication performed. Props projection generation
and a one-command rich feature generator remain explicitly outside this delivery.

flake.nix

@@ -21,6 +21,7 @@
             pkgs.git
             pkgs.jujutsu
             pkgs.gnutar
+            pkgs.util-linux
           ];
           buildPhase = ''
             runHook preBuild
@@ -63,6 +64,8 @@
             runHook preInstall
             mkdir -p "$out"
             install -Dm644 nix/checked-package.nix "$out/share/checked-package.nix"
+            substitute nix/checked-candidate.nix "$out/share/checked-candidate.nix" \
+              --replace-fail '@nixpkgs@' '${pkgs.path}'
             cp --reflink=auto --recursive grammar "$out/grammar"
             cp --reflink=auto --recursive proto "$out/proto"
             cp --reflink=auto --recursive dist "$out/dist"