feat(lora): state a pinned userPrefs preset as the unset region's intent

[NomDeTom]

Fixes #11506.

A vendor/community build can pin a modem preset with USERPREFS_LORACONFIG_MODEM_PRESET while leaving USERPREFS_CONFIG_LORA_REGION unset, so the user still picks their own region. Both NodeDB::installDefaultConfig() and Channels::initDefaultLoraConfig() apply the pin, so a fresh flash comes up as region UNSET + the pinned preset.

A stock install comes up as region UNSET + the LONG_FAST placeholder, and nothing in FromRadio separated the two. Clients therefore treat every unset-region node as factory-fresh and replace its preset with the region default the moment the user picks a region — so a mesh pinned to SHORT_TURBO loses each new node to LONG_FAST or LONG_TURBO, silently. Filed against the clients as meshtastic/Meshtastic-Android#6704 and meshtastic/Meshtastic-Apple#2273; neither can fix it without a signal from us.

Change

getRegionPresetMap() emits an UNSET entry when, and only when, the build pins a preset, stating that preset as both the group's sole entry and its default_preset.

Build	UNSET in region_groups	Client reads
Stock	absent	unconstrained, preset is a placeholder
Pinned	present, single preset	the build intends this preset

Stock builds are unchanged on the wire, so this is inert unless a build actually pins a preset.

Intent, not enforcement. Since #11496 supportsPreset() accepts any known preset while the region is unset, and the radio is held silent either way, so the device still honours whatever the user or an admin sets. The map does not narrow that, and the test asserts it.

Costs one group slot and one region slot on pinned builds only (6→7 of max_count:8, 34→35 of 38). Exhaustion is logged and degrades to the existing unconstrained behaviour.

Testing

./bin/run-tests.sh -e native -f test_radio — 22/22 green in both build shapes, since the #ifdef means one run only covers one of them:

• Stock — test_regionPresetMap_unsetCarriesUserprefsIntent asserts UNSET is absent from the map entirely.
• Pinned — with USERPREFS_LORACONFIG_MODEM_PRESET set to SHORT_TURBO in userPrefs.jsonc and a full rebuild: asserts the single-preset UNSET group, its default, and that supportsPreset() still accepts other real presets while unset.

test_regionPresetMap_coversAllRegionsWithinBounds and _matchesRegionTable are updated for the extra entry on pinned builds.

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features

  • Added support for builds with a pinned modem preset, exposing it through the UNSET region option.
  • The pinned preset is used as both the default and only available choice.

• Bug Fixes

  • Improved handling when the region preset map reaches capacity, preventing invalid entries from being advertised.

• Tests

  • Added coverage confirming pinned-preset behavior and ensuring standard builds continue to omit the UNSET option.

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📥 Commits

Reviewing files that changed from the base of the PR and between ca29fe7 and 814db95.

📒 Files selected for processing (2)

• src/mesh/RadioInterface.cpp
• test/test_radio/test_main.cpp

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

• src/mesh/RadioInterface.cpp
• test/test_radio/test_main.cpp

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📝 Walkthrough

Walkthrough

The radio preset map now advertises a pinned modem preset under UNSET when configured. Tests verify the synthetic entry, its licensing and acceptance behavior, map counts, and omission from stock builds.

Changes

Pinned modem preset intent

Layer / File(s)	Summary
Add the UNSET preset-map entry src/mesh/RadioInterface.cpp	Configured builds add a single-entry UNSET group with the pinned preset as its default. The entry preserves the UNSET licensing flag and checks map capacity.
Validate pinned and stock map behavior test/test_radio/test_main.cpp	Tests cover map counts, region-table comparisons, pinned preset details, broad unset-region acceptance, and stock-build omission. The new test is registered in the suite.

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

Merge Risk: ⚪ Minimal · up to 814db

The change communicates pinned preset intent for unset regions while preserving stock behavior and user flexibility; no actionable merge-blocking risk remains beyond normal checks and review.

Possibly related issues

• meshtastic/Meshtastic-Android#6704 — The firmware change supplies the pinned-preset signal that the Android client can use.
• meshtastic/Meshtastic-Apple#2273 — The firmware change supplies the pinned-preset signal that the Apple client can use.

Suggested labels: enhancement

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly states the primary change: reporting a pinned user preference preset for the unset LoRa region.
Description check	✅ Passed	The description explains the problem, implementation, wire behavior, capacity impact, and test coverage, although template attestations are not checked.
Linked Issues check	✅ Passed	The implementation satisfies issue #11506 by signaling pinned presets for UNSET without enforcing them and preserving stock-build behavior.
Out of Scope Changes check	✅ Passed	The source and test changes directly support the linked issue and PR objectives; no unrelated changes are evident.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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Actionable comments posted: 1

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Inline comments:
In `@src/mesh/RadioInterface.cpp`:
- Around line 749-760: Reduce the newly added comments to no more than one or
two lines each: update the UNSET intent explanation in
src/mesh/RadioInterface.cpp at lines 749-760, and the count-test rationale,
UNSET exclusion rationale, and UNSET behavior rationale in
test/test_radio/test_main.cpp at lines 295-297, 343-346, and 390-393
respectively. Preserve the tests and behavior; only shorten the comments.

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📥 Commits

Reviewing files that changed from the base of the PR and between f57ee0b and ca29fe7.

📒 Files selected for processing (2)

• src/mesh/RadioInterface.cpp
• test/test_radio/test_main.cpp