fix(codex): bound parent subagent previews

[dwaxe]

Refs #2300

This removes the quadratic parent-copy path for Codex provider subagents.

• keep canonical child activity in the provider-subagent timeline
• limit parent snapshots to the latest 200 activities, 4 KiB per activity, and 32 KiB total
• preserve UTF-8 boundaries and nested-parent updates without copying complete descendant logs

Regression coverage exercises large, nested, and multibyte child histories.

[greptile-apps]

Greptile Summary

The PR bounds Codex parent sub-agent previews while retaining canonical child activity in provider-subagent timelines.

• Limits parent previews by activity count, per-item UTF-8 byte size, and aggregate log size.
• Rebuilds tool-call previews without serializing potentially large structured payloads.
• Adds coverage for large prompts, errors, nested histories, recent-activity selection, and multibyte text.

Confidence Score: 4/5

The PR appears safe to merge after the non-blocking test-shape issue is cleaned up.

The production bounding path preserves canonical child activity and no concrete runtime regression remains, but two new regression tests violate the repository’s deterministic, conditional-free test-body convention.

Files Needing Attention: packages/server/src/server/agent/providers/codex-app-server-agent.test.ts

Important Files Changed

Filename	Overview
packages/server/src/server/agent/providers/codex-app-server-agent.ts	Adds UTF-8-safe truncation and bounded parent-preview projection while preserving separate canonical child events.
packages/server/src/server/agent/providers/codex-app-server-agent.test.ts	Adds broad regression coverage for bounded previews, with two new test bodies using prohibited inline conditionals.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart LR
  C[Canonical child timeline] --> P[Select latest 200 activities]
  P --> I[Bound each activity to 4 KiB]
  I --> L[Curate parent log]
  L --> B[Bound parent log to 32 KiB]
  B --> R[Emit root parent snapshot]
  C --> S[Emit full provider-subagent activity]

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[greptile-apps]

Conditional test-body guards

These inline if guards mix assertion mechanics with branching and repeat the repository-prohibited conditional test-body pattern. Move snapshot narrowing into a helper or use deterministic assertions so failures remain direct.

Rule Used: # Code Review Pattern Reference: Slop, Tests, Feat... (source)

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