Add an overlay-first pure-upsert route for overlay_publish=small_deltas so bounded changed-file overlays can publish before recursive exact inbound-frontier expansion falls through to containment.
The route reuses existing scratch seed, extract/resolve, postpass, delta metadata, preserved-inbound, and overlay publish helpers. It is gated to pure upserts in FAST-or-higher modes within the existing exact changed/affected path caps, and falls through to the existing exact/containment paths on failure.
Avoid a duplicate failed overlay generation when overlay-first reaches the publish step and fails; exact upsert skips the second overlay publish attempt and continues to canonical exact fallback.
Add a wide-inbound pipeline canary proving a changed Leaf with four unchanged callers now publishes incremental_overlay before frontier_too_large and active overlay BFS still sees CallerA -> Leaf.
Validation: make -f Makefile.cbm -j8 build/c/test-runner; CBM_ONLY_SUITE=pipeline build/c/test-runner (321 passed); CBM_ONLY_SUITE=mcp build/c/test-runner (166 passed); scripts/check-source-safety.sh on touched files; git diff --check.
Signed-off-by: Andrew Hundt <ATHundt@gmail.com>
Andrew Hundt
4e8ef6018e