docs: changelog entry for the conformance extraction

README needs no change: it documents gate behaviour rather than module
structure, names no moved symbol, and behaviour is unchanged by design.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: agarwal-ishaan

CHANGELOG.md

@@ -2,6 +2,23 @@
 
 ## Unreleased
 
+### Refactor
+
+- **conformance**: extract the four generation safety gates out of
+  `code_generator_main` into a new `pdd.conformance` package (`gate_errors`,
+  `directives`, `surface`, `test_churn`, `interface_check`,
+  `declared_surface`), taking `code_generator_main.py` from 5,879 to 2,033
+  lines. Behaviour is unchanged: every definition moved as an exact source
+  slice, and all 91 moved symbols are re-exported from
+  `pdd.code_generator_main` using the redundant-alias form, so existing
+  `from pdd.code_generator_main import ...` call sites keep resolving.
+  `sync_main`, `sync_orchestration`, `one_session_sync`, `cmd_test_main` and
+  `agentic_test_generate` can now catch `ArchitectureConformanceError`,
+  `PublicSurfaceRegressionError`, `TestChurnError` and `ProseOutputError`
+  from `pdd.conformance.gate_errors` without importing the generation
+  pipeline. Pinned by user story `pdd_generation_gates_preserved`, whose
+  Non-Oracle excludes PDD's internal module organisation.
+
 ### Feat
 
 - **test**: add `pdd test --from-story <story>` to compile a story's sibling