Validate source equivalence and layered scaling

docs/roadmap/implementation.md

@@ -461,6 +461,28 @@ checker and full race suite.
 
 ## Stage 9: Validate cross-feature consistency and scaling
 
+**Completed 2026-09-29.** A compact public matrix now checks equivalent host,
+native, byte, reader, and mapping inputs; tier-local repetition versus cross-tier
+reuse; reader consumption; and safe diagnostics/effective/history output after
+secret replacement. Engine tests verify exact occurrence accounting across
+imports, shared glob/source limits, and the mixed-source CLI ceiling. Rendering
+now indexes source labels once per explanation instead of scanning all records
+for every location. Loading and passive context ownership were reviewed against
+ADR 0008; no handles or background work are retained by queries.
+
+On Linux amd64 with `-benchmem` and 100 ms samples, the 512-entry assembly-only
+composition measured about 3.5 ms/op (the earlier post-index baseline was about
+3.3 ms), and recursive overlay about 2.2 ms/op (about 12 ms at the first-stage
+handoff before subsequent provenance work). The 128-application owned assembly
+remained about 0.30 ms/op versus 6.35 ms/op for copy-preserving application.
+End-to-end layered measurements were about 7.15 ms/op for 512 broad catalog
+entries, 2.59 ms/op for 128 small tiers, 3.27 ms/op for 128 alternating subtree
+replacements, 1.86 ms/op for 64 imported native defaults, and 1.36 ms/op for
+64 retained-history applications. Allocations grew roughly with these fixture
+sizes. I/O, sorting, decoding, callbacks, and retained output contribute to
+full-path cost; these observations are not timing gates or an unconditional
+complexity guarantee. The everyday checker and full race suite passed.
+
 1. Consolidate a small semantic equivalence matrix across host, native, bytes,
    readers, and mappings, using equivalent logical inputs and contexts. Cover
    strict conflict versus intentional precedence and version-path preservation;