[BUG][CORE] Fix #18963: stop reusing anonymous inline schemas across different parent schemas

[rvlasveld]

Summary

Fixes #18963.

Two different component schemas (e.g. Item and Issue) each declare an anonymous (untitled) inline user object with identical members. The generator de-duplicates them by structural content, so both ItemDto and IssueDto end up referencing a single ItemUserDto. This is wrong: the two objects are conceptually distinct, and the reused name (ItemUserDto) is misleading in the Issue context.

Root cause: matchGenerated() in InlineModelResolver matches by serialized content alone, ignoring whether the schema has a title. Anonymous inline schemas have context-derived names (Item_user, Issue_user) that are arbitrary — reusing one parent's model for another's context forces a misleading name.

Fix: Add a title guard in matchGenerated: if a schema has no title, return null immediately (don't reuse). Only titled schemas represent intentionally shared named types.

This makes the runtime cache consistent with the two other dedup paths in the same file that already gate on title:

• flatten() pre-populate step (seeds only titled component schemas into the signature cache)
• deduplicateComponents() post-pass (skips untitled schemas: if (schema.getTitle() == null) continue)

Changes

• InlineModelResolver.java — add title guard in matchGenerated()
• InlineModelResolverTest.java — add regression test for [BUG] [Kotlin] DTOs for components of different components are conflated if they have the same members #18963; update testInlineSchemaSkipReuseSetToFalse to reflect new default (anonymous schemas now get separate models)
• docs/customization.md — document the new default behaviour

Existing tests unaffected

All resolveInlineModelDeduplicates* regression tests use titled schemas (Widget, StorageBackend, Container Mapping, Deletion Request) — they continue to deduplicate correctly.

Note on samples

This is a core behaviour change. Samples that happen to contain specs with structurally-identical anonymous inline objects across different parents will gain additional model classes. Sample regeneration is required before merge (./bin/generate-samples.sh).

---

Alternative (opt-in, no breaking change): #23975 adds SKIP_ANONYMOUS_SCHEMA_REUSE=true as an inlineSchemaOption (default off, no sample churn). Use that PR if a default behaviour change is undesirable.

Test plan

• InlineModelResolverTest#resolveAnonymousInlineSchemaNotReusedAcrossParents — direct [BUG] [Kotlin] DTOs for components of different components are conflated if they have the same members #18963 regression (Item/Issue with identical anonymous user inline object)
• InlineModelResolverTest#testInlineSchemaSkipReuseSetToFalse — updated: both meta_200_response and mega_200_response now created (anonymous schemas no longer reused by default)
• All resolveInlineModelDeduplicates* tests — titled-schema dedup still works
• Regenerate samples: ./bin/generate-samples.sh + ./bin/utils/ensure-up-to-date

🤖 Generated with Claude Code

[cubic-dev-ai]

No issues found across 3 files

_{Re-trigger cubic}