fix(server): make synthetic CSI opt-in only (sibling fix to #937) (#979)

Background

Issue #937 in the cognitum-v0 appliance repo flagged that the
`cognitum-csi-capture` systemd unit shipped `--simulate` by default,
silently serving synthetic CSI tagged as production telemetry on
`/api/v1/sensor/stream`. That's a textbook trust-eroding pattern — the
single most-cited "where's the real data?" evidence external reviewers
(#943, #934) point at when they call the project AI-slop.

A grep across THIS tree surfaced the exact same anti-pattern in three
places:

  docker/docker-compose.yml:27        # auto (default) — probe ESP32, fall back to simulation
  docker/docker-entrypoint.sh:14      # CSI_SOURCE — data source: auto (default), ...
  main.rs:6435                        info!("No hardware detected, using simulation"); "simulate"

The sensing-server's `auto` source resolver at main.rs:6425-6440
silently fell back to synthetic with only an `info!` log line as the
signal. Downstream consumers calling `/api/v1/sensing/latest` or
`/ws/sensing` had no in-band way to know they were being served fake
data.

Fix

`auto` now refuses to fall back. When neither ESP32 UDP nor host WiFi
is detected, the server logs a clear `error!` explaining the situation
and exits 78 (EX_CONFIG). The error message names the two ways to
proceed: provision real hardware, or set `--source simulated` /
`CSI_SOURCE=simulated` explicitly. Existing operators who already use
`--source simulated` (or its legacy `simulate` alias) are unaffected —
the alias is preserved for back-compat.

Docker entrypoint comment, docker-compose comment, and the Tauri
desktop app's source-default path also updated to reflect the new
posture. The desktop app keeps its `simulated` default because it's
an explicit demo product — the value passed downstream is the
*explicit* `simulated`, not `auto`, so the server tags it correctly
and never lies about its data source.

Validation

  cargo build  -p wifi-densepose-sensing-server --no-default-features
  cargo test   -p wifi-densepose-sensing-server --no-default-features
  → 122 / 122 pass, build clean (existing pre-fix warnings unchanged).

Deployment

⚠ Breaking change for unattended deployments that relied on the
`auto → simulated` silent fallback. That is exactly the failure mode
this PR fixes: pretending to serve real sensing data when the source
is fake. Operators who genuinely want demo mode set
`CSI_SOURCE=simulated` explicitly; the error message and the
docker-compose comment both point them there.

docker/docker-compose.yml

@@ -24,10 +24,13 @@ services:
     environment:
       - RUST_LOG=info
       # CSI_SOURCE controls the data source for the sensing server.
-      # Options: auto (default) — probe for ESP32 UDP then fall back to simulation
+      # Options: auto (default) — probe for ESP32 UDP then host WiFi; **fail
+      #                           hard with exit 78 if neither is detected**.
+      #                           Synthetic data is no longer a silent fallback
+      #                           (issue #937 fix) — operators must opt in.
       #          esp32          — receive real CSI frames from an ESP32 on UDP port 5005
       #          wifi           — use host Wi-Fi RSSI/scan data (Windows netsh)
-      #          simulated      — generate synthetic CSI data (no hardware required)
+      #          simulated      — explicitly generate synthetic CSI for demo mode
       - CSI_SOURCE=${CSI_SOURCE:-auto}
       # MODELS_DIR controls where the server scans for .rvf model files.
       # Mount a host directory and set this to make models visible:

docker/docker-entrypoint.sh

@@ -11,7 +11,16 @@
 #      docker run ruvnet/wifi-densepose:latest --model /app/models/my.rvf
 #
 # Environment variables:
-#   CSI_SOURCE   — data source: auto (default), esp32, wifi, simulated
+#   CSI_SOURCE   — data source. Valid values:
+#                    auto       — try ESP32 then Windows WiFi, **fail-loud if no
+#                                 real hardware is detected** (issue #937 fix:
+#                                 the server no longer silently falls back to
+#                                 synthetic data — that's now opt-in only).
+#                    esp32      — listen for UDP CSI on the configured port.
+#                    wifi       — Windows-native WiFi capture.
+#                    simulated  — explicit demo mode with synthetic CSI.
+#                  Default is `auto`. Set CSI_SOURCE=simulated when you want
+#                  fake data tagged as such; never set it implicitly.
 #   MODELS_DIR   — directory to scan for .rvf model files (default: data/models)
 set -e