merge: sync Rongsong's scheduler-framework into chatbot

Full merge of origin/scheduler-framework (scheduler-core restructure,
failover-adoption, WAL_JOB_DISPATCH, apiserver backend health/heartbeat,
build-time versioning, bug-1673/1676/1678/1679/1680).

Conflict resolution:
- scheduler: adopt Rongsong's scheduler-core architecture (driver loop,
  queue project/picker fields, resource bug-1569 fix)
- worker/controller_connector.c: keep Rongsong's reconnect/rejoin
  structure, PORT our bug-1509 resend_job_status onto the rejoin success
  path (his reconnect didn't re-report job state)
- apiserver backend: take Rongsong's health/heartbeat (supersedes our
  e505066 circuit breaker)
- group.c: keep our bug-1513 comment
- misc: take theirs for additive fixes (go_build versioning,
  test_group.c, persist.c RUSAGE_UPDATE, FilterRows bug-1680)

NOTE: our scheduler fixes (bug-1494 family dispatch-fail requeue,
PEND-reason classification) are NOT in Rongsong's branch — needs
verification/porting onto scheduler-core (separate follow-up).

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

src/flake.nix

@@ -16,6 +16,46 @@
         if builtins.hasAttr "shortRev" self
         then self.shortRev
         else self.dirtyShortRev;
+      # NOTE (build-time-versioning task 2.2, remediation round): unlike
+      # myCommitId (a genuinely flake-level, eval-time concept sourced from
+      # self.shortRev/self.dirtyShortRev), the build timestamp is NOT
+      # computed here. An earlier attempt used `builtins.toString
+      # builtins.currentTime` at this exact spot -- but builtins.currentTime
+      # is stripped entirely under a flake's default pure evaluation
+      # ("error: attribute 'currentTime' missing"), so `nix build
+      # .#xcecore_debug` (no --impure, the documented canonical command)
+      # failed at evaluation. Fixed by moving the build-time computation
+      # into each derivation's own build phase instead (xce.nix/xcecli.nix
+      # `preConfigure`, via stdenv's bundled `date -u`) -- see those files.
+      # Nothing build-time-related needs to be threaded through the flake
+      # or nixSupport/default.nix any more; only myCommitId still does.
+      # dirty-content-fingerprint task 2.2: myDirtyFingerprint is a new,
+      # independent eval-time value alongside myCommitId (myCommitId's own
+      # computation above, including its self.dirtyShortRev-derived -dirty
+      # suffix, is NOT touched by this addition). Unlike build_time
+      # (builtins.currentTime, stripped under pure-eval -- see the note
+      # above), self.narHash is a genuine flake self-introspection field
+      # with no pure-eval trap: it is reachable and content-sensitive with
+      # no --impure needed (empirically re-confirmed live: editing a
+      # tracked file changes it, reverting reproduces the original value
+      # exactly). self.narHash's own string form is SRI-style base64
+      # ("sha256-<base64>="), not hex, so it is rehashed via
+      # builtins.hashString "sha256" (which DOES return a base16/hex
+      # digest) and truncated to 8 hex chars to match the dev-loop path's
+      # format (xce-build.sh task 2.1's `sha256sum | cut -c1-8`). Resolves
+      # to empty on a clean tree, mirroring myCommitId's own
+      # hasAttr "shortRev" branch immediately above (a clean tree only has
+      # self.shortRev; a dirty tree also has self.dirtyShortRev).
+      # KNOWN, ACCEPTED LIMITATION (see research.md "Nix path accepts the
+      # untracked-file blind spot"): self.narHash does not reflect
+      # brand-new untracked files unless they are git-add-staged first --
+      # deliberately not engineered around here (would require adding git
+      # as a nix sandbox dependency, an explicit prior architectural
+      # decision this feature does not revisit).
+      myDirtyFingerprint =
+        if builtins.hasAttr "shortRev" self
+        then ""
+        else builtins.substring 0 8 (builtins.hashString "sha256" self.narHash);
     in
       flake-utils.lib.eachSystem supportedSystems (
         system: let
@@ -25,7 +65,7 @@
           ];
           pkgs = import nixpkgs { inherit overlays system;};
           xpkgs = import ./nixSupport/default.nix {
-            inherit pkgs myCommitId;
+            inherit pkgs myCommitId myDirtyFingerprint;
           };
           appImageScriptContent = builtins.readFile ./tools/appimage/entry.sh;
           appImageEntryPackage = pkgs.writeShellApplication {