fix(factory): keep cosmetic UI gaps nonblocking

[walker-tx]

Summary

• define material versus presentation-only scope uncertainty at the coordinator gate
• require research and writing agents to hedge undocumented UI chrome and continue
• preserve pauses for unresolved authentication, endpoint, credential, security, capability, feasibility, and source-conflict questions
• add prompt-contract regressions for the Box failure mode

Verification

• GOFLAGS='-ldflags=-linkmode=external' bash factory/tests/run.sh (11/11 tests)
• git diff --check
• independent review: no findings