fix(pallet-tfgrid): enforce node_certification in farming policy limits

[sameh-farouk]

Summary

Enforces the node_certification field in FarmingPolicyLimit — Diy nodes on farms with certified-only policy limits now correctly fall back to a matching default policy instead of receiving the certified-only policy.

Also fixes get_default_farming_policy() which ignored node/farm certification entirely when selecting fallback defaults.

Problem

Per the spec:

Certification. If set, only certified nodes can get this policy. Non certified nodes get a default policy.

This was never enforced. On mainnet, farm 2995 (GoldAndGreen) has 4 Diy nodes (2 currently online) earning certified-level farming rewards on policy 3 instead of a Diy default policy.

Root Cause

Two issues in pricing.rs:

1. No certification check in the FarmingPolicyLimit path of get_farming_policy() — limits only checked end, cu, su, node_count

2. get_default_farming_policy() ignored certification — when limits were exhausted (or now when certification fails), it picked the highest-ranked default regardless of the node's actual certification. Per the spec, default selection should consider both node and farm certification:

   • First: highest farm cert + certified nodes
   • Then: highest farm cert + non-certified nodes
   • Then: no farm cert + certified nodes
   • Last: no certification at all

Fix

• Add node_certification check at the start of the limits path
• Replace get_default_farming_policy() with get_default_farming_policy_for(node, farm) that filters by both node_certification and farm_certification
• This affects all 5 fallback paths: certification check (new), end expired, cu exceeded, su exceeded, node_count exhausted

Tests (115 pass, 0 fail)

3 new test cases:

• diy_node_gets_default_policy_when_limit_requires_certification — Diy node on Gold farm with node_certification=true gets policy 1 (Diy+Gold) instead of policy 3 (Certified+Gold)
• certified_node_gets_limited_policy_when_limit_requires_certification — Certified node correctly receives the limited policy (positive case)
• diy_node_gets_limited_policy_when_no_certification_required — node_certification=false doesn't filter (no restriction)

All 112 existing tests continue to pass.

Mainnet Impact

Currently affected: 4 Diy nodes on farm 2995 affected by the bug (wrong policy assigned) with farming_policy_id: 3 (certified-only policy, no end date) But only 3 are currently earning wrong rewards.

• 6768, 6968 and 6656 Last seen within days
• 7873 last seen 243 days ago

This fix only affects future policy assignments. Existing nodes need a storage migration or manual set_node_certification call to trigger re-evaluation through get_farming_policy.

Fixes #429

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 4 complexity · -2 duplication

Metric	Results
Complexity	4
Duplication	-2

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