Make context snapshot text rendering consistent (#44976)

## What changed

- Use the same text rendering for model instructions in request settings and Responses Lite developer content.
- Make `rewrite_known_segments` emit plain tags for recognized guidance, including collaboration and multi-agent instructions. Check message roles and complete tag boundaries so lookalike user or tool content stays visible, and retain generated compaction summaries.
- Normalize working-directory, workspace-root, and temporary paths in permission guidance while preserving policy differences.
- Separate text clipping from normalization and retain eight lines at each end of long sections, with fingerprints for omitted content. Update affected snapshots.

## Testing

Add regression coverage for instruction rendering across transports, literal and rewritten guidance, malformed and lookalike tags, compaction summary preservation, and permission path normalization that keeps policy changes detectable.

GitOrigin-RevId: 33b052911323c73b0387d650478f9cc3370fd001

codex-rs/core/src/session/snapshots/codex_core__codex_tests__fork_startup_context_then_first_turn_diff.snap

@@ -9,11 +9,11 @@ Scenario: First request after fork when startup preserves the parent baseline, t
 00:message/developer:
     <PERMISSIONS_INSTRUCTIONS>
 01:message/user:
-    <ENVIRONMENT_CONTEXT:cwd=<CWD>>
+    <ENVIRONMENT_CONTEXT>
 02:message/user:
     fork seed
 03:message/developer[2]:
     [01] <PERMISSIONS_INSTRUCTIONS>
-    [02] <collaboration_mode>Fork turn collaboration instructions.</collaboration_mode>
+    [02] <COLLABORATION_MODE>
 04:message/user:
     after fork