Fix Block wiring, model migration and workflow readiness

[sdevil7th]

Summary

Fix the workflow authoring defects found during the text-to-image workflow review:

• Create nested-capable V2 Blocks through the native dialog; preserve crossing wires, nested contents, selected controls and labels, and surface save errors inside the dialog.
• Validate cycles on executable dependencies, including expanded internal reconnects and mirrored ports. Keep named-node explanations for genuine loops.
• Block missing required inputs inside collapsed Blocks in both Auto and Custom memory, using current registry declarations even for older saved nodes.
• Preview removal of unused, untouched generated outputs during model changes; preserve connected, configured and preview-bound interfaces. Deliberately edited creation interfaces become explicit contracts.
• Render scalar input editors alongside sockets, name their connection source, and preserve saved fallback values through disconnect.
• Place ordinary inserted nodes in free space without moving existing nodes.
• Distinguish graph readiness from Auto resource qualification.

Public controls and sockets remain available. Existing saved libraries are not rewritten. Auto qualification and custom-code consent remain intact.

Paired backend

Backend contract commit: a0d29db8484f8f06f9d42f6782634cd66e1ac996 (also pinned in client CI).
Paired backend PR: sdevil7th/MoDiff#6. It includes the generated client bundle from this source commit.

Validation

• npm ci: passed; zero reported vulnerabilities.
• Final npm run check: passed (format, lint, types, catalog, unit/contracts, build, bundle limits and shell module identity).
• npm run check:ui: shared controls 3/3; full mocked run 225/230. All five initial failures were fixed and passed in a focused rerun of eight affected scenarios, including native creation/model-change persistence and scalar sockets. No browser failures remain unaddressed.
• Regression unit tests cover required-input blocking in Auto/Custom, expanded internal reconnects, preserved crossing wires and explicit interfaces, and connected-output protection.
• Production bundle cold startup from the backend: no JavaScript or asset-loading errors.
• An intermediate quality run encountered an unrelated Linux /proc cleanup-test race (ESRCH); the final complete rerun passed without changing that test.

Live backend evidence:

• Copy of the original saved Qwen Block: reviewed Qwen → Z-Image migration, Save/reload, then a 512×512 Custom-memory run at nine steps completed in 34 seconds. Raw and custom palette outputs both rendered.
• Partial loader/denoiser/decoder grouping around external Encode Inputs retained all seven execution edges. Real mouse disconnect/reconnect no longer reports a false loop. Save/reload and Auto execution completed in 33 seconds.
• Original disconnected encoder workflow disables Run after reopening. Florence exposes task, prompt and output type in both canvas and inspector.

These are focused live checks, not all-model qualification. FLUX Auto refusal remains correct without an accepted exact recipe; SDXL prompt adherence is not changed.

Compatibility and review

• New Block creation writes V2. Existing V1 readers and lifecycle browser coverage remain; there is no automatic library migration.
• No new dependencies, executor, provider, or trust boundary. No credentials, model weights, generated media, local paths or raw private evidence are committed.
• Native creation is deferred. Measured compressed startup is about 624.2 KiB and deferred code about 248.1 KiB; budgets have small documented increases for the added validation/editor logic.
• User guide updated. Gallery/template qualification and release acceptance were not rerun because no template or model qualification is claimed.
• AI assistance: Codex implementation, diff review and verification. Human maintainer review remains pending.