Explicit masterfeats/feats removal

TOPDATA_HARDENING_CONTRACT.md

@@ -42,12 +42,16 @@ One concrete example already observed:
 - validation in `internal/topdata/topdata.go` still hard-fails specifically for
   `topdata/data/masterfeats/base.json` if `output` is missing
 
-That mismatch proves the current methodology is stale:
+That mismatch proved the current methodology was stale:
 
 - the runtime/build side treats `masterfeats` like a generic dataset
 - the validator still treats it like a special namespace with explicit required
   metadata
 
+Current status: the output-name mismatch has been fixed for `masterfeats` and
+the equivalent `feat` base dataset rule by sharing the derived output-name rule
+between discovery and validation.
+
 This same category of problem appears in several other places.
 
 ## Findings From Current Audit
@@ -67,17 +71,17 @@ This same category of problem appears in several other places.
 Some of these are legitimate dataset-shape differences. Others are stale
 special-cases that should be generalized.
 
-### 2. `masterfeats` still carries outdated explicit validation rules
+### 2. `masterfeats` carries dataset-specific invariants
 
-`validateMasterfeatsBaseFile()` currently requires:
+`validateMasterfeatsBaseFile()` currently enforces:
 
-- `output == masterfeats.2da`
+- explicit `output == masterfeats.2da` when `output` is authored
 - specific required columns
 - `masterfeats:` row keys
 
 The key-prefix and column requirements may still be valid dataset invariants.
-The `output` requirement is not clearly justified anymore when generic dataset
-discovery already computes a default output name from location.
+The stale requirement that `output` must be authored has been removed; validation
+now shares the same derived default output-name rule as native discovery.
 
 ### 3. Migration still seeds explicit dataset exceptions
 
@@ -128,7 +132,9 @@ keep inheriting brittle assumptions.
 
 ### Work Item 1: Remove outdated `masterfeats.output` hard requirement
 
-Investigate and likely change `validateMasterfeatsBaseFile()` so:
+Status: implemented.
+
+`validateMasterfeatsBaseFile()` now:
 
 - missing `output` is accepted when generic dataset discovery can derive the same
   output name deterministically