Use when the user wants to manually flush a deferred-commit queue from a prior or interrupted chain. Reads .hyperflow/commits-queue/manifest.json, fast-forwards the staging branch onto the user's branch, deletes staging, clears the queue. Recovery interface when a chain crashed before its Step 4 auto-flush ran. Trigger with /hyperflow:flush, "flush pending commits", "flush queue", "apply staged commits", "where are my commits".