AdminModule: don't return the device private key to remote config reads

[caveman99]

A get_config for SECURITY_CONFIG copies config.security straight into the response:

res.get_config_response.payload_variant.security = config.security;

config.security includes private_key, the device identity key used to derive PKC shared
secrets. For a request that arrived over the mesh (from != 0), that response is sent back
over the air, so the private key leaves the device. Only the local owner needs it, and only
for backup.

Zero private_key in the SECURITY_CONFIG response when the request is remote. Local admin
clients (BLE/USB/TCP) set from == 0 and still receive the full config, so the backup/restore
path is unchanged. This mirrors the existing writeSecret() redaction used for
network.wifi_psk a few cases up.

On admin_key: I evaluated redacting it too and left it. Those entries are public keys ("the
public key authorized to send admin messages"), not secret material, and a legitimate remote
admin may want to read the configured admin set. private_key is the only field whose exposure
escalates to identity compromise. Zeroing admin_key for remote would be a one-line addition in
the same block if that trust-set disclosure is judged worth closing.

Tests (test_admin_session_repro): a remote SECURITY_CONFIG response decodes to an empty
private_key; a local (from == 0) response still carries the 32-byte key, so the redaction is
remote-specific rather than a blanket wipe.

Summary by CodeRabbit

• Security Enhancements
  • Remote security configuration responses no longer include the device identity private key.
  • Local security configuration access continues to include the private key when authorized.
• Tests
  • Added coverage verifying that sensitive keys are redacted for remote requests and preserved for local requests.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 4308487 and 57a61c7.

📒 Files selected for processing (3)

• src/modules/AdminModule.cpp
• test/support/AdminModuleTestShim.h
• test/test_admin_session_repro/test_main.cpp

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📝 Walkthrough

Walkthrough

SECURITY_CONFIG responses now redact the device identity private key for remote admin requests. Test utilities and deterministic tests verify that remote replies omit the key while local replies preserve its 32-byte value.

Changes

Security Config Redaction

Layer / File(s)	Summary
Remote private-key redaction src/modules/AdminModule.cpp	Remote SECURITY_CONFIG responses zero the private-key bytes and set the field size to 0; local responses retain the existing key.
Remote and local response tests test/support/AdminModuleTestShim.h, test/test_admin_session_repro/test_main.cpp	The test shim exposes queued replies, and tests decode SECURITY_CONFIG responses to verify remote omission and local retention of the private key.

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

Suggested labels: bugfix

Suggested reviewers: jp-bennett

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title is concise and accurately summarizes the main change: redacting the device private key from remote config reads.
Description check	✅ Passed	The description covers the bug, fix, rationale, and tests, and only misses the repository's checklist-style attestations.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch security-config-redact

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