user://atlas_cache/ is one directory for every worktree gate run, live
capture driver, and real play session, and T-1183's Tier-2/3 lookup
short-circuits BEFORE test_mode's silent-no-op IPC — so a warm shared
cache delivers real canvases into tests written against 'nothing ever
arrives'. Caught live: a concurrent GJ380c Global capture flipped the
two before-any-canvas viewer tests in another worktree's push gate.
Adds disk_cache_root_override on StepCanvasViewer (threads into
StepCanvasRequest's existing test-injection-only seam; production
leaves it empty) and routes every direct viewer construction in the
viewer + legend suites through a _make_viewer() helper pinning an
isolated root. First slice of T-1193's viewer test seam; screen-built
viewers still share the default root (noted on T-1193).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
jpmschweitzerandClaude Fable 5
9ac98542d1