Rewrite reference docs as current state; record the style rule

Reference, guidelines and plan documents describe what is and what will be.
Retirement stories, resolved-risk narration and against-the-alternative
argument moved out or were cut; reports keep that material.

What survives the cut is the mechanism that can bite again (driving side is a
country-level property) and the condition that would change a decision (a
permanently installed, car-powered panel), both stated generally.

Also removes a duplicated Japan section from a bad edit.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013kj58Jugkic783b8ZrtTVZ

docs/ORIN-RUNTIME.md

@@ -44,9 +44,9 @@ have taken their share.
 
 Four rules follow.
 
-**The cloud LLM is load-bearing.** [OVERVIEW.md](../OVERVIEW.md) puts reasoning in
-the cloud. That decision is what makes a local voice stack fit at all — moving the
-LLM on-device collapses this budget entirely. It is not a free choice to revisit.
+**Reasoning runs in the cloud.** The local voice stack fits only because the LLM
+is not resident. An on-device LLM and the voice stack do not coexist in this
+budget.
 
 **Size Whisper by vocabulary, not by benchmark.** In-car commands are a narrow,
 predictable set. `large` buys accuracy this application cannot spend, at a cost
@@ -156,10 +156,10 @@ Same protocol, same receiver. The receiver starts playback on the first chunk,
 appends as more arrive, and finishes on the terminator — which is what Android's
 `AudioTrack` streaming mode does natively.
 
-**What must not be built:** an utterance as a single response body with a
-"download the file, then play the file" player. That works today and forecloses
-streaming permanently. Whether the TTS we land on streams is still open, so the
-transport must not assume either way.
+⚠ **Never ship an utterance as a single response body with a "download, then
+play" player.** It works, and it forecloses streaming permanently — the receiver
+has no way to begin before the last byte. The chunk boundary is what keeps both
+TTS modes available.
 
 ### The transport is testable with no real TTS
 
@@ -171,10 +171,8 @@ completely. Voice quality is irrelevant to every one of those.
 ### Ducking is the tablet's job
 
 Android's `AUDIOFOCUS_GAIN_TRANSIENT_MAY_DUCK` ducks other applications' audio —
-Spotify included — for the duration of a request, then restores it. This is the
-mechanism every navigation app already uses, and it is less work than the PipeWire
-policy it replaces. Cross-application ducking is a solved problem on the tablet
-and would have been a bespoke one on the Orin.
+Spotify included — for the duration of a request, then restores it. Cross-
+application ducking is native on the tablet.
 
 ### The microphone stays on the Orin
 
@@ -188,6 +186,5 @@ With no tablet connected the Orin can still hear — the mic is local — but ca
 speak. The voice stack expires or drops pending utterances rather than queueing
 them unboundedly or blocking on a sink that may never arrive.
 
-The consequence to accept: **unplug the tablet and the car has no voice.** That is
-tolerable because unplugging it also removes the music, so the tablet was already
-load-bearing for audio. Speech does not make it more so.
+**The tablet is required for any audio at all** — it is both the media source and
+the speech sink.