Make PM submit tolerate assignment replica lag

[wallscaler]

Summary

• Makes per-miner submit recover tier/seq from the signed pm-* challenge id when per_miner_assignments is not visible yet.
• Re-materializes the assignment row idempotently before verification, so the ledger catches up without rejecting valid work.
• Keeps invalid and cross-miner pm-* challenge ids rejected.

Why

Miners were intermittently seeing assignment_required_fetch_challenges_first immediately after fetching a private CNF. Root cause: /per-miner/cnf wrote per_miner_assignments, but immediate /v1/agents/submit could read from a lagging replica/app state and miss the row.

Verification

• Claude adversarial review: no blockers; requested decoupling from legacy scan flag and cross-miner negative coverage, both addressed.
• UV_LINK_MODE=copy uv run --extra publisher python publisher_verify.py -> PASS all 149 checks
• UV_LINK_MODE=copy uv run --extra publisher python assigned_lane_verify.py -> PASS all 15 checks
• UV_LINK_MODE=copy uv run --extra publisher python weights_verify.py -> PASS all 32 checks
• UV_LINK_MODE=copy uv run --extra publisher python -m compileall scaffold publisher_verify.py assigned_lane_verify.py weights_verify.py -> PASS
• git diff --check -> PASS

Launch Note

This is safe to deploy independently. It does not change scoring math. It only removes a false-negative PM submit rejection caused by assignment-ledger visibility lag.