gizmoduck: row 270 (264c, #1775) round 4 for sage-3073 and sage-3078: rows 270 and 271 rebased onto 25c09f19f (row 203 plus the O2 docs); mosaic-config.mjs keeps 203's federation key and both compaction keys; BUILD.md round 4 with the range-diff, the three merged files and C1 after 203; not run

agents/gizmoduck/work/queue-270/BUILD.md

@@ -465,3 +465,42 @@ runs cli compactions-launch.test.mjs (600 s). Per sage-3038, the slot goes to Me
 - The ledger's cursor map still grows when the agent deletes and recreates streams, by at most the
   cap per collection. Each deletion of a stream with a cursor is store-incomplete for good. This is
   the known limit that the bus reads the ledger whole (round 2).
+
+## Round 4: rebase onto row 203 (sage-3073)
+
+Rows 270 and 271 are rebased onto origin/refactor 25c09f19f (sage-3078): row 203 (FED R2) at
+a4da4e6df, plus three docs-only commits for the O2 design (BUILD-LOG.md, docs/SESSIONS.md and
+docs/plans/2026-10-21_q195-writing-editor.md, none of them in either manifest). The new branch is
+gizmoduck/row270-271-r4. gizmoduck/row271-r2 stays at b9da7697f. The old
+merge-base was 0cbe2e9b3, and the rebase moved 28 commits.
+
+`git range-diff 0cbe2e9b3..b9da7697f 25c09f19f..HEAD~1` shows 26 commits
+unchanged. Round 2 and round 3 differ, and only in scripts/mosaic-config.mjs:
+
+- The allowlist keeps 203's literal and adds both keys after it:
+  `["configVersion", "environment", "dataRoot", "execution", "console", "federation"].concat(["compactionReadBytes", "compactionStreams"])`.
+  203 changed packages/cli/tests/stack-release-fixture.mjs, and its LOADER_OLD replace is now at
+  :301 (rounds 2 and 3 say :300). It matches the literal with `"federation"`, which is still
+  intact before the `.concat`.
+- The output has 203's `federation` line, then the two `Object.hasOwn` lines.
+
+Rows 203, 270 and 271 also all touch scripts/test-config.sh, scripts/stack-release.sh and
+packages/cli/tests/stack-release.test.mjs. Those merged without conflict, and the hunks are far
+apart:
+
+- test-config.sh: 203's federation cases start at :194. Mine are at :266-:281, after the
+  no-console case.
+- stack-release.sh: 203 changed config_checks at :1078-:1097. Row 271's change is COUNTED at
+  :420, still the line 271's BUILD.md cites.
+- stack-release.test.mjs: 203 changed :1468 and :1582. Row 271's LISTED is still at :861 and T46
+  at :913.
+
+203 widens config_checks to run the target loader for a `federation` key as well as `console`.
+It still does not run the loader for compactionReadBytes or compactionStreams, so C1 stands as
+written.
+
+`mutants.py check` passes: every anchor matches once. The restore hashes in round 3's table are
+unchanged, because 203 touches none of those four files. No test pins a sha256 of mosaic-config.mjs,
+test-config.sh, stack-release.sh or stack-release.test.mjs.
+
+Nothing has run on this base yet. The combined gate is sage-3073 item 4, on Sage's CLEAR.