The translate card, pointed the other way, and a call that no longer happens

Phase 28's step (b): both remaining items are about direction, and both had
a wrong answer that looked right.

isTranslation could not simply be read backwards. readsAsEnglish is a
deliberately low bar — Latin letters, not swamped by another script — which
every Portuguese sentence clears as easily as English does, so swapping its
two halves would have called every genuine Portuguese correction inside a
Portuguese document a translation. The flipped direction uses sentenceLang
from doclang.go instead, where English has its own curated marker list and
has to out-evidence the pair language to win. The English-document path is
untouched; reconcilePending carries the verdict to ask the question the
right way round.

The tap-through's whole observable change is a model call that stops
happening. /suggestions/{id}/translate now recovers the explanation's
language by re-running targetFor rather than assuming the pair, which gives
today's answer everywhere except the case that was broken: the Portuguese
writer whose explanation already arrived in Portuguese, previously
round-tripped through the model into Portuguese again. It answers "" there,
and the client's existing `res.translation.trim() || explanation` fallback
seeds the bubble with the explanation itself — no frontend change at all.
It deliberately does not render that explanation into English on the
grounds that English is technically the other half: an unasked-for
rendering into the language she is practising is noise, not a seed.

Tests pin both directions of the detector, with Portuguese-in-Portuguese as
the case the file exists for, plus four handler tests through the real
/check and /translate paths — including the skipped seed asserting the
model was never called, and the learning_pair zh learner whose English
explanation still renders into Chinese.

Left of the phase: (c) the garden's language tagging and read-aloud.

Claude-Session: https://claude.ai/code/session_01GJHNvirh7Hzhc9RL3HAvz7

internal/suggestions/language.go

@@ -28,16 +28,35 @@ import (
 //     common words a sentence in that language can hardly avoid and an English
 //     sentence has no reason to contain.
 
-// isTranslation reports whether this edit is her own language rendered into
-// English, rather than a correction to her English. Both halves must hold: the
-// quoted span reads as the pair language, and what Petal offers back reads as
-// English. The second half matters — a Chinese span rewritten into different
-// Chinese is something else entirely, and Petal has no business calling it a
-// translation.
-func isTranslation(original, replacement, pairLang string) bool {
+// isTranslation reports whether this edit is a rendering of one language into
+// the other, rather than a correction. Both halves must hold: the quoted span
+// reads as one language, and what Petal offers back reads as the other. The
+// second half matters — a Chinese span rewritten into different Chinese is
+// something else entirely, and Petal has no business calling it a translation.
+//
+// Which way it points follows the document (Phase 28). In an English document
+// the translate card is her language rendered into English — she reached for a
+// sentence she couldn't say yet, and Petal said it for her. In a document she
+// wrote in her own language the useful card is the mirror image: an English
+// sentence she dropped into her Portuguese, rendered into Portuguese. Asking the
+// English-document question there would label nothing, and the card would file
+// as a correction to prose that was never wrong.
+//
+// The flipped direction cannot be the same test read backwards. `readsAsEnglish`
+// is a low bar on purpose — Latin letters, not swamped by another script — which
+// every Portuguese sentence also clears, so using it on the *original* would
+// call every genuine Portuguese correction a translation. The flipped test
+// instead uses the sentence-level vote from doclang.go, where English has its
+// own marker list and has to out-evidence the pair language to win.
+func isTranslation(original, replacement, pairLang, docLang string) bool {
 	if strings.TrimSpace(original) == "" || strings.TrimSpace(replacement) == "" {
 		return false
 	}
+	if normalizeDocLang(docLang) == docLangPair {
+		p := normalizePairLang(pairLang)
+		return sentenceLang(original, p) == docLangEnglish &&
+			sentenceLang(replacement, p) == docLangPair
+	}
 	return readsAsPairLang(original, pairLang) && readsAsEnglish(replacement)
 }