chore: untrack tsconfig.tsbuildinfo, and hold the CI baseline the way the local gate does

`frontend/tsconfig.tsbuildinfo` was swept into the previous commit by a `git add
-A`. It is a machine-local incremental artifact carrying absolute Windows paths,
no lane reads or regenerates it, and it was already stale in the commit that added
it — it does not list the contract test that same commit created. Untracked, and
`*.tsbuildinfo` ignored, because the day anything does start rewriting it a green
gate would leave a tracked file dirty: the exact hazard the basedpyright baseline
just got a guard for.

And CI ran bare basedpyright while the local lane gained that guard, so a
burn-down would have been green on the server and red on the developer's machine
over the same tree. Two gates, one tree, one answer.

.gitea/workflows/check.yml

@@ -96,10 +96,19 @@ jobs:
       # The ninth lane (E27 S3). Run from backend/ so it resolves exactly as the local lane does —
       # pyrightconfig.json's include/extraPaths are relative to the config, but the baseline is
       # found relative to the working directory. New errors fail; the ~200 pre-existing ones are in
-      # .basedpyright/baseline.json and burn down epic by epic.
+      # .basedpyright/baseline.json and burn down epic by epic. Matching is per (file, rule, column
+      # span) plus a count, so a new error of the SAME shape in a file where a sibling was just
+      # fixed is absorbed — burn the hot files down first.
+      #
+      # The second step is not redundant. basedpyright TIGHTENS the baseline in place when the count
+      # drops, with no --writebaseline, and CI throws its workspace away — so without this a
+      # burn-down is green here and red on the developer's `siftlode check`, which has the same
+      # guard. Two gates over one tree must not answer differently.
       - name: basedpyright
         run: python -m basedpyright --project pyrightconfig.json
         working-directory: backend
+      - name: basedpyright baseline is committed
+        run: git diff --exit-code -- backend/.basedpyright/baseline.json
       - name: pytest
         run: python -m pytest
         working-directory: backend

.gitignore

@@ -37,3 +37,7 @@ backups/
 Thumbs.db
 .idea/
 .vscode/
+
+# TypeScript incremental build artifacts — machine-local, absolute-path-bearing, and no gate lane
+# reads or regenerates them, so a committed one is stale from the commit that adds it.
+*.tsbuildinfo