Add support for RFC 2132 Message option in NAK handling

[ColinMcInnes]

If the dhcpcd server sends Option 56 (message) as part of a DHCPv4 NAK, pass it on to the exit hook environment so it can be acted on if necessary.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Team

Run ID: 4d17d77c-8b87-48c0-8e3d-061077bec664

📥 Commits

Reviewing files that changed from the base of the PR and between 324f1e1 and 860739c.

📒 Files selected for processing (2)

• src/dhcp.c
• src/dhcp.h

🚧 Files skipped from review as they are similar to previous changes (2)

• src/dhcp.h
• src/dhcp.c

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Walkthrough

DHCP NAK responses now store RFC 2132 option 56 text in DHCP state. make_env exports the text as message for NAK hooks, and the hook documentation describes the variable.

Changes

DHCP NAK message export

Layer / File(s)	Summary
Capture and manage NAK messages src/dhcp.h, src/dhcp.c	The DHCP state stores the NAK message. NAK handling captures the DHO_MESSAGE option, and DHCP cleanup frees the stored text.
Export and document the message src/script.c, hooks/dhcpcd-run-hooks.8.in	make_env exports the stored message as message=<value> for NAK events, then clears it. The hook documentation describes the variable.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to 86073

This localized change passes the DHCPv4 NAK message option to the exit-hook environment; no actionable merge-blocking risk remains beyond normal checks and review.

Sequence Diagram(s)

sequenceDiagram
  participant DHCP_Server as DHCP server
  participant dhcp_handledhcp
  participant dhcp_state
  participant make_env
  participant Script_Hook as script hook
  DHCP_Server->>dhcp_handledhcp: Send NAK with DHO_MESSAGE
  dhcp_handledhcp->>dhcp_state: Store message text
  dhcp_handledhcp->>dhcp_state: Drop lease
  make_env->>dhcp_state: Read message text
  make_env->>Script_Hook: Export message=<value>
  make_env->>dhcp_state: Free and clear message

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🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 3 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies support for the RFC 2132 Message option during DHCP NAK handling, which matches the main changeset.
Description check	✅ Passed	The description accurately states that DHCPv4 NAK Option 56 values are passed to the exit hook environment.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[ColinMcInnes]

recheck