fix rfswitch_table cross-file merge; drop now-stale checker warning

Three CodeRabbit findings on 09e0d390c, addressed together since #2
and #3 are the same root cause:

1. PortduinoGlue.cpp: require an exact "DIO<n>" match when parsing
   rfswitch_table.pins. sscanf's %d stops at the first non-digit, so
   "DIO5invalid" silently parsed as DIO5 at runtime even though
   ConfigCheck.cpp's static validator (exact match against
   kRfSwitchPins) already rejected it - checker and loader disagreed.

2. PortduinoGlue.cpp: reset all 5 pin slots and all 8 mode rows before
   applying a table, rather than only overwriting what the new table
   mentions. A later config.d file that omitted a mode a prior file
   had set (e.g. only redefining MODE_TX) let the earlier file's
   MODE_RX leak through, contradicting "last file wins" - the rule
   every other Lora: key already follows.

3. ConfigCheck.cpp: with #2 fixed, rfswitch_table behaves like any
   other cross-file key, so removed the special-cased ERROR in
   checkCrossFileOverlap ("These do NOT override each other... OR of
   every table") - it described the pre-fix OR-accumulation bug and
   is no longer accurate. Falls through to the generic "last file
   wins" INFO now. Renamed/repurposed the rfswitch-sticky fixture to
   rfswitch-last-wins and updated its assertion (was rc=1 asserting
   the old error text, now rc=0 asserting the generic info) and the
   fixtures README.

Verified: bin/test-config-check.sh GREEN 69/69 against an isolated
native build, including the renamed assertion.

bin/test-config-check.sh

@@ -402,12 +402,12 @@ assert "config.d overrides are reported" 0 configd-conflict/config.yaml check \
 	"files define a 'Lora:' section" \
 	"The file loaded last wins" \
 	"Result: 0 errors,"
-# Switch tables are the one place "last wins" is false: the loader only ever writes
-# HIGH, so the effective table is the OR of every file. Proven with --output-yaml.
-assert "switch tables across files do not override" 1 rfswitch-sticky/config.yaml check \
-	"These do NOT override each other" \
-	"a HIGH from an earlier file survives a later file that sets LOW" \
-	"Enable exactly one"
+# rfswitch_table follows "last file wins" like every other Lora: key: no special-cased
+# error, just the standard cross-file-overlap info.
+assert "rfswitch tables across files: last one wins" 0 rfswitch-last-wins/config.yaml check \
+	"'Lora.rfswitch_table' is set in 2 files" \
+	"The file loaded last wins" \
+	"Result: 0 errors,"
 
 echo
 echo "--check takes precedence over --output-yaml:"

src/platform/portduino/ConfigCheck.cpp

@@ -915,18 +915,6 @@ void checkCrossFileOverlap(const PathIndex &paths, const std::map<std::string, s
         if (coveredByAncestor)
             continue;
 
-        // The one place "last wins" is untrue: the loader only ever writes HIGH, so the effective
-        // table is the OR of every table loaded -- a switch state belonging to none of them.
-        if (entry.first == "Lora.rfswitch_table") {
-            findings.push_back({kError, across, 0,
-                                "'Lora.rfswitch_table' is set in " + std::to_string(entry.second.size()) + " files (" +
-                                    describeOwners(entry.second) +
-                                    "). These do NOT override each other: the loader only ever writes HIGH, so a HIGH "
-                                    "from an earlier file survives a later file that sets LOW there, and the radio ends "
-                                    "up driving the OR of every table. Enable exactly one"});
-            continue;
-        }
-
         findings.push_back({kInfo, across, 0,
                             "'" + entry.first + "' is set in " + std::to_string(entry.second.size()) + " files (" +
                                 describeOwners(entry.second) + "). The file loaded last wins"});

src/platform/portduino/PortduinoGlue.cpp

@@ -1095,14 +1095,23 @@ bool loadConfig(const char *configPath)
             }
             if (yamlConfig["Lora"]["rfswitch_table"]) {
                 portduino_config.has_rfswitch_table = true;
+                // A later file's table fully replaces an earlier one, matching "last file wins"
+                // for every other Lora: key, rather than leaving omitted pins/modes as carryover.
+                for (int i = 0; i < 5; i++)
+                    portduino_config.rfswitch_dio_num[i] = -1;
+                for (int m = 0; m < RFSW_MODE_COUNT; m++) {
+                    portduino_config.rfswitch_mode_present[m] = false;
+                    portduino_config.rfswitch_mode_high[m] = 0;
+                }
                 const YAML::Node table = yamlConfig["Lora"]["rfswitch_table"];
 
                 // Store the DIO number as written; the slot it maps to is per-radio. Anything
-                // not spelled "DIO<n>" leaves the slot unused.
+                // not spelled exactly "DIO<n>" (trailing junk included) leaves the slot unused.
                 for (int i = 0; i < 5; i++) {
                     const std::string name = table["pins"][i].as<std::string>("");
                     int dioNum = 0;
-                    if (sscanf(name.c_str(), "DIO%d", &dioNum) == 1 && dioNum >= 0 && dioNum <= INT8_MAX)
+                    if (sscanf(name.c_str(), "DIO%d", &dioNum) == 1 && dioNum >= 0 && dioNum <= INT8_MAX &&
+                        name == "DIO" + std::to_string(dioNum))
                         portduino_config.rfswitch_dio_num[i] = (int8_t)dioNum;
                 }
 

test/fixtures/portduino-config/README.md

@@ -182,13 +182,11 @@ the last-loaded file is reset to its default - here `config.yaml` sets
 The load order within `config.d/` comes from the filesystem, so the report warns
 rather than assuming alphabetical order.
 
-`rfswitch-sticky/` covers the one place where "the file loaded last wins" is false,
-and it documents a firmware bug rather than a configuration mistake. Its `config.d/`
-holds two switch tables; the last one loaded sets `MODE_RX` LOW on both pins, but the
-loader only ever writes HIGH and never writes LOW back, so the HIGH from the earlier
-file survives and the effective table is the OR of both. Verified with
-`meshtasticd --output-yaml`. Until the loader is fixed, `--check` reports this as an
-error and tells you to enable exactly one.
+`rfswitch-last-wins/` covers `Lora.rfswitch_table` across two `config.d/` files. It
+follows the same "last file loaded wins" rule as every other `Lora:` key - the loader
+resets a table's pins and mode rows before applying a replacement, so an earlier
+file's `MODE_RX` setting cannot leak through a later file that omits it. `--check`
+reports this as the standard cross-file-overlap info, not a special-cased error.
 
 ## Running these as a normal boot
 

test/fixtures/portduino-config/rfswitch-last-wins/config.d/b-second.yaml

@@ -0,0 +1,7 @@
+# Sets MODE_RX LOW on both pins. Whichever of this file and a-first.yaml the filesystem
+# returns last should fully replace the other's table, per "last file wins".
+Lora:
+  Module: lr1121
+  rfswitch_table:
+    pins: [DIO5, DIO6]
+    MODE_RX: [LOW, LOW]

test/fixtures/portduino-config/rfswitch-last-wins/config.yaml

@@ -0,0 +1,4 @@
+# Primary config for the rfswitch_table last-wins case. The two files in config.d/
+# each define a Lora.rfswitch_table; the one loaded last should fully replace it.
+General:
+  ConfigDirectory: config.d/

test/fixtures/portduino-config/rfswitch-sticky/config.d/b-second.yaml

@@ -1,9 +0,0 @@
-# FAULT, and it is a firmware bug rather than a typo. This file is loaded LAST and says
-# MODE_RX is LOW on both pins, but the loader only ever writes HIGH and never writes
-# LOW back, so the HIGH from a-first.yaml survives. The effective table is the OR of
-# both files -- a switch state that neither file asked for. Verified with --output-yaml.
-Lora:
-  Module: lr1121
-  rfswitch_table:
-    pins: [DIO5, DIO6]
-    MODE_RX: [LOW, LOW]

test/fixtures/portduino-config/rfswitch-sticky/config.yaml

@@ -1,4 +0,0 @@
-# Primary config for the sticky-switch-table case. The two files in config.d/ each
-# define a Lora.rfswitch_table.
-General:
-  ConfigDirectory: config.d/