Deepen safe live fixtures for branch-heavy file and transfer behavior

[altaywtf]

Outcome

Add deterministic, reversible live fixtures that exercise the highest-value conditional file responses and transfer state or mutation paths without touching arbitrary account data.

Raised from #108 and the priority gaps in docs/READINESS.md.

Scope

• Rare or parameter-conditioned file response branches.
• File task success, failure, and terminal-state behavior where safe fixtures can produce it deterministically.
• Transfer status transitions and reversible mutation paths that are not covered by the current live target.
• A successful upload-backed event torrent fixture if it naturally falls out of the same controlled setup.

Acceptance criteria

• Fixture setup uses only explicitly owned, SDK-prefixed resources and never selects arbitrary private files.
• Every mutation has deterministic cleanup, including failure and interruption paths.
• Tests exercise the built package from dist/** through the existing live harness.
• Conditional response and error branches assert decoded SDK contracts, not only raw HTTP success.
• Repeated runs are idempotent or fail closed with actionable fixture diagnostics.
• docs/TESTING.md and docs/READINESS.md describe the added fixture requirements and remaining gaps.
• Targeted live proof passes with fresh runtime tokens.

Verification

• vp run verify
• vp run lint:package
• vp run test:compat
• Targeted pnpm test:live:fresh -- ... runs for the changed live targets.

Non-goals

Password reset, 2FA enable or disable, account destruction, revoke-all sessions, and other lockout-capable auth/account mutations remain sandbox-only until a sacrificial account exists.