Right-size nRF52 heap tiers after 2.8.0 heap-exhaustion field reports (#10898)

* Right-size nRF52 heap tiers after 2.8.0 heap-exhaustion field reports

Field reports on 2.8.0 show nRF52840 devices at 99% heap (114/115 KB)
within minutes of boot; operator new asserts on OOM, so these devices
are one allocation from a reboot. The 2.8.0 cache sizing ladders gave
nRF52 the largest non-PSRAM tiers on the assumption that a BLE-only
part has a roomy heap - the arena is actually ~125 KB shared with the
FreeRTOS task stacks.

Per-target retiers (nRF52840 unless noted):
- Traffic Management cache 1000 -> 250 entries (10 KB -> 2.5 KB); the
  unclassified fallthrough drops 1000 -> 400 to match the classic-ESP32
  tier (also affects RP2040/RP2350)
- Warm node store 200 -> 100 entries (8 KB -> 4 KB); the non-XXAA
  fallthrough drops 320 -> 100 so an unclassified RAM-constrained part
  can't boot-allocate 12.8 KB
- MESSAGE_HISTORY_LIMIT 20 -> 10 (text pool 4.4 KB -> 2.2 KB), the tier
  classic ESP32 already ships
- MAX_RX_TOPHONE 32 -> 16, shrinking the static packet pool 70 -> 54
  slots (~6.6 KB of .bss returned to the heap arena)
- PacketHistory hash index off arch-wide (1 KB); O(n) over 240 records
  is negligible at LoRa packet rates
- OLEDDISPLAY_REDUCE_MEMORY arch-wide (~1 KB OLED back buffer); the five
  TFT variants -U it because TFTDisplay.cpp needs buffer_back for
  dirty-window diffing
- Drop the stale "for testing" 1024-entry TMM override on T1000-E

Measured on rak4631: heap arena grows 124,572 -> 131,180 B and boot
allocations drop ~15.7 KB, roughly +22 KB free heap on the field-report
device class.

Migration: the nRF52840 warm flash ring replays through place() (LRU),
so the newest 100 identities survive the shrink; the file backend
rejects oversized snapshots cleanly (new test covers this). Native
suites pass (536/536 Docker, 13/13 native-macos warm store); rak4631,
heltec-mesh-node-t114 (TFT) and tracker-t1000-e build green.

* Drop stale OLEDDISPLAY_REDUCE_MEMORY -U on t114 / mesh-solar-tft

Only USE_TFTDISPLAY variants (t1, t096, wismeshtap) compile
TFTDisplay.cpp and need the lib's buffer_back; t114 and mesh-solar-tft
render through the meshtastic-st7789 driver, which handles the
reduced-memory configuration fine - as #10894 (merged from develop)
already established by defining the flag there. Remove the -U guard and
the per-variant -D (redundant with the arch-wide define in nrf52_base
on this branch). Both variants verified building.

src/mesh/mesh-pb-constants.h

@@ -17,6 +17,12 @@
 #ifndef MAX_RX_TOPHONE
 #if defined(ARCH_ESP32) && !(defined(CONFIG_IDF_TARGET_ESP32C3) || defined(CONFIG_IDF_TARGET_ESP32S3))
 #define MAX_RX_TOPHONE 8
+#elif defined(NRF52840_XXAA)
+// Each slot is a ~340 B MeshPacket in the static pool (Router.cpp MAX_PACKETS_STATIC), so 32 slots
+// cost ~11 KB of .bss on the RAM-tightest platform (2.8.0 field reports: 99% heap). 16 still doubles
+// the 8 classic ESP32 has shipped with for years; drops start when a stalled phone/serial client has
+// 16 packets queued.
+#define MAX_RX_TOPHONE 16
 #else
 #define MAX_RX_TOPHONE 32
 #endif
@@ -126,7 +132,10 @@ static inline int get_max_num_nodes()
 // Keyed on the NRF52840_XXAA build flag, not ARCH_NRF52: the latter (from
 // architecture.h via configuration.h) isn't defined this early in every include
 // chain. Backed by the raw-flash ring below LittleFS - see WarmNodeStore.h.
-#define WARM_NODE_COUNT 200
+// 100 (was 200): the RAM cache is 40 B/entry calloc'd from the ~115 KB heap
+// arena, which 2.8.0 field reports showed at 99% use; 120 hot + 100 warm
+// identities still covers meshes well past the hot cap.
+#define WARM_NODE_COUNT 100
 #elif (defined(CONFIG_IDF_TARGET_ESP32S3) && defined(BOARD_HAS_PSRAM)) || defined(ARCH_PORTDUINO)
 #define WARM_NODE_COUNT 2000 // PSRAM-equipped ESP32-S3 / native host; warm cache in PSRAM (~80 KB)
 #elif defined(CONFIG_IDF_TARGET_ESP32S3) || defined(CONFIG_IDF_TARGET_ESP32C6) || defined(CONFIG_IDF_TARGET_ESP32P4)
@@ -136,10 +145,11 @@ static inline int get_max_num_nodes()
 #elif defined(ARCH_RP2040)
 #define WARM_NODE_COUNT 150 // RP2040 (264 KB) / RP2350 (520 KB): bounded so warm.dat write fits the 8s watchdog (#10746)
 #else
-// nRF52840 is handled explicitly above (200, raw-flash ring). Any other nRF52 (non-XXAA) and any
-// future non-ESP32/non-RP LittleFS part fall through to this 320 default - flag for review if such a
-// RAM-constrained nRF52 target is ever added.
-#define WARM_NODE_COUNT 320 // other LittleFS-backed parts (e.g. non-nRF52840 nRF52)
+// nRF52840 is handled explicitly above (raw-flash ring). Any other nRF52 (non-XXAA) and any future
+// non-ESP32/non-RP LittleFS part lands here. Reviewed after the 2.8.0 nRF52840 heap-exhaustion
+// reports: fail small (match nRF52840) so an unclassified RAM-constrained part can't boot-allocate
+// 12.8 KB; RAM-rich targets should opt up explicitly in their variant.
+#define WARM_NODE_COUNT 100 // other LittleFS-backed parts (e.g. non-nRF52840 nRF52)
 #endif                      // platform
 #endif                      // WARM_NODE_COUNT
 
@@ -177,11 +187,16 @@ static inline int get_max_num_nodes()
 #define TRAFFIC_MANAGEMENT_CACHE_SIZE 500 // 512 KB+ SRAM, no PSRAM (S3/C6/P4): ~5 KB heap (#10705)
 #elif defined(ARCH_ESP32)
 #define TRAFFIC_MANAGEMENT_CACHE_SIZE 400 // classic ESP32 / S2 / C3: tightest free heap, ~4 KB (#10705)
+#elif defined(NRF52840_XXAA)
+// Keyed on NRF52840_XXAA (not ARCH_NRF52) for the same include-order reason as WARM_NODE_COUNT above.
+// The 256 KB part shares its ~115 KB heap arena with SoftDevice and the FreeRTOS task stacks; 2.8.0
+// field reports hit 99% heap use with the old 1000-entry (~10 KB) cache. 250 entries (2.5 KB) still
+// tracks >2x the 120-node hot store; LRU victim recycling absorbs busier meshes.
+#define TRAFFIC_MANAGEMENT_CACHE_SIZE 250
 #else
-// nRF52 (incl. nRF52840) and RP2040/RP2350 fall through here - there is no nRF/RP branch above,
-// by design. These parts have no ESP32-style WiFi+BLE coexistence eating the heap, so the larger
-// 1000-entry (~10 KB) cache fits: nRF52840 is BLE-only on 256 KB RAM; RP2040/RP2350 have 264/520 KB.
-#define TRAFFIC_MANAGEMENT_CACHE_SIZE 1000 // nRF52 / RP2040 / RP2350 / other non-ESP32
+// RP2040/RP2350 and anything unclassified land here: match the classic-ESP32 tier rather than
+// defaulting large. RAM-rich targets should opt up explicitly in their variant.
+#define TRAFFIC_MANAGEMENT_CACHE_SIZE 400
 #endif
 #endif // TRAFFIC_MANAGEMENT_CACHE_SIZE