core: respect environment_context for network access in prompt (#3136)

[AjayKumbham]

Summary

• Align system instructions with actual runtime context by relying on the initial environment_context for network_access, rather than assuming defaults.

What

• Update codex-rs/core/prompt.md to:
  • Direct the agent to use environment_context.network_access and sandbox_mode to reason about capabilities.
  • Avoid language that speculates about network availability when network_access is enabled.
  • Fall back to defaults only if environment_context is missing.

Why

• Fixes incorrect reasoning where the agent stated “Since the repository might not have network access…” despite user config enabling network access (network_access = true).
• Resolves issue #3136 by ensuring messaging matches the configured sandbox policy and network settings communicated via environment_context.

How

• Documentation-only change to codex-rs/core/prompt.md. No runtime logic modified.
• The core already emits an initial environment_context message including network_access; this change instructs the model to respect it.

Impact

• User-facing reasoning and messages are now consistent with the configured network access.
• No functional behavior changes to tools, sandboxing, or execution paths.

Testing

• No code changes; no unit tests updated.
• Verified docs compile and style remains consistent.
• Manual validation: with network_access = true under workspace-write, the agent’s guidance should reflect that outbound network is available.

Files Changed

• codex-rs/core/prompt.md

Related Issues

• Fixes #3136.

Checklist

• Focused, minimal change
• Matches TUI and style guidelines
• No unrelated refactors
• References linked issue
• No new lints or formatting deviations

[github-actions]

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[AjayKumbham]

I have read the CLA Document and I hereby sign the CLA