feat(client): DmService narrate loop + FakeDmTransport (all branches tested)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

client/scripts/net/dm_service.gd

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+class_name DmService
+extends RefCounted
+## The client narrate loop (charter §2: the client owns the loop and consumes
+## text). Posts the canon log to /dm/narrate through an injected transport,
+## returns the prose to display and the [FACT:] tags to harvest. On ANY failure
+## it returns an authored fallback line — never an error. It harvests facts
+## only; the Narrator has no authority over disposition or moves, so those tags
+## are dropped even if the model emits them (§6). narrate() does not mutate the
+## log — the caller applies the returned facts, keeping the state write explicit.
+
+var _transport: DmTransport
+var _fallback: FallbackLibrary
+
+
+func _init(transport: DmTransport, fallback: FallbackLibrary) -> void:
+	_transport = transport
+	_fallback = fallback
+
+
+func narrate(canon_log: CanonLog) -> NarrateResult:
+	var resp: DmResponse = await _transport.post_json(
+		"/dm/narrate", {"canon_log": canon_log.to_dict()})
+	if not resp.transport_ok or resp.status != 200 \
+			or typeof(resp.body) != TYPE_DICTIONARY or not resp.body.has("prose"):
+		return NarrateResult.fallback(_fallback.narrator_line())
+	var extracted := TagExtractor.extract(str(resp.body["prose"]))
+	return NarrateResult.new(extracted["clean_text"], extracted["facts"], false)

client/scripts/net/dm_service.gd.uid

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+uid://b467yu4cut0hp