Finish Phase 22: the half of Petal that works with the tunnel down

Grammar lite, the false-friend list, the daily invitation and the offline
miscollocations — the four remaining §5–§6 items, all client-side and all
alive on a box that cannot reach the model.

The offline collocations forced a schema change. `type` had been doubling
as the answer to "which engine found this" — `mechanics` meant offline —
and that stops being true the moment an offline rule proposes a
collocation. Migration 0013 adds `source` (llm | local) and every pass now
scopes its DELETE by engine; without it the coach silently wiped every
offline chunk on the page. Existing rows backfill by type, so a pre-0013
collocation row is claimed as the coach's, which it was: the offline list
did not exist yet.

The rule pack is hand-curated rather than mined, and the entries left out
are the point — `married with` is wrong until "married with children",
`arrive to` wants at or in depending on the noun. A pack running on every
keystroke must not correct correct writing.

Claude-Session: https://claude.ai/code/session_016y6gyuHkQXPiEuW8RGQyua

internal/suggestions/offline_test.go

@@ -0,0 +1,203 @@
+package suggestions
+
+import (
+	"encoding/json"
+	"net/http"
+	"testing"
+
+	"gitea.parodia.dev/drwily/petal/internal/db"
+)
+
+// The offline rule pack and the LLM now share the collocation family, which is
+// the point: the writer sees one rail and is never told which engine spoke. What
+// makes that safe is `source` — each pass replaces only its own rows. These tests
+// pin the two ways that could go wrong, both of which the old type-scoped DELETEs
+// would have hit.
+
+// pendingOfType counts the pending rows of one family in a response body.
+func pendingOfType(got []db.Suggestion, typ string) []db.Suggestion {
+	var out []db.Suggestion
+	for _, s := range got {
+		if s.Type == typ {
+			out = append(out, s)
+		}
+	}
+	return out
+}
+
+// TestOfflineCollocationFilesAsCollocation proves a miscollocation the rule pack
+// found is stored in the collocation family (so accepting it plants a garden
+// card, exactly as the coach's would) while still being marked as locally found.
+func TestOfflineCollocationFilesAsCollocation(t *testing.T) {
+	srv, docID, _ := newTestServer(t, &stubClient{response: `{"suggestions":[]}`})
+
+	got := postMechanics(t, srv, docID, `[
+		{"from":0,"to":13,"original":"do a decision","replacement":"make a decision","explanation":"pairing","type":"collocation"},
+		{"from":20,"to":27,"original":"the the","replacement":"the","explanation":"doubled word","type":"mechanics"}
+	]`)
+	if len(got) != 2 {
+		t.Fatalf("want both findings, got %+v", got)
+	}
+	coll := pendingOfType(got, db.SuggestionTypeCollocation)
+	if len(coll) != 1 {
+		t.Fatalf("want 1 collocation, got %+v", got)
+	}
+	if coll[0].Source != db.SuggestionSourceLocal {
+		t.Errorf("offline finding should be source=local, got %q", coll[0].Source)
+	}
+	if mech := pendingOfType(got, db.SuggestionTypeMechanics); len(mech) != 1 {
+		t.Fatalf("want 1 mechanics finding, got %+v", got)
+	}
+}
+
+// TestUnknownLocalTypeFallsBackToMechanics: a family the offline pass isn't
+// allowed to claim (or an older client sending none at all) must land in
+// mechanics. Otherwise a stray label would smuggle a row into an LLM family,
+// where nothing would ever replace it.
+func TestUnknownLocalTypeFallsBackToMechanics(t *testing.T) {
+	srv, docID, _ := newTestServer(t, &stubClient{response: `{"suggestions":[]}`})
+
+	got := postMechanics(t, srv, docID, `[
+		{"from":0,"to":5,"original":"aaaaa","replacement":"bbbbb","explanation":"x","type":"voice"},
+		{"from":6,"to":11,"original":"ccccc","replacement":"ddddd","explanation":"y"}
+	]`)
+	if len(got) != 2 {
+		t.Fatalf("want 2 findings, got %+v", got)
+	}
+	for _, s := range got {
+		if s.Type != db.SuggestionTypeMechanics {
+			t.Errorf("offline finding claimed family %q; only mechanics/collocation are allowed", s.Type)
+		}
+	}
+}
+
+// TestCoachDoesNotWipeOfflineCollocations is the collision the source column
+// exists for: the LLM collocation pass replaces the collocation family, and the
+// rule pack's share of that family has to survive it. Before `source`, running
+// the coach silently deleted every offline chunk on the page.
+func TestCoachDoesNotWipeOfflineCollocations(t *testing.T) {
+	client := &stubClient{response: `{"suggestions":[
+		{"original":"apple","replacement":"an apple","explanation":"article","type":"collocation"}
+	]}`}
+	srv, docID, _ := newTestServer(t, client)
+
+	// The seeded doc is "I has two apple." — the coach's flag anchors on "apple"
+	// at [10,15], so the offline finding is given a span well clear of it. Two
+	// findings fighting over the same characters is a different rule (see
+	// TestOfflineCardWinsSpanCollision); this test is about the DELETE.
+	postMechanics(t, srv, docID, `[
+		{"from":0,"to":5,"original":"do a decision","replacement":"make a decision","explanation":"pairing","type":"collocation"}
+	]`)
+
+	rec := do(t, srv, http.MethodPost, "/docs/"+docID+"/collocation", "")
+	if rec.Code != http.StatusOK {
+		t.Fatalf("collocation pass: code=%d body=%s", rec.Code, rec.Body)
+	}
+	var got []db.Suggestion
+	if err := json.Unmarshal(rec.Body.Bytes(), &got); err != nil {
+		t.Fatalf("decode: %v", err)
+	}
+
+	var local, llm int
+	for _, s := range pendingOfType(got, db.SuggestionTypeCollocation) {
+		if s.Source == db.SuggestionSourceLocal {
+			local++
+		} else {
+			llm++
+		}
+	}
+	if local != 1 {
+		t.Errorf("the coach wiped the offline collocation: local=%d, got %+v", local, got)
+	}
+	if llm != 1 {
+		t.Errorf("want the coach's own flag alongside it: llm=%d, got %+v", llm, got)
+	}
+}
+
+// TestOfflinePassReplacesItsOwnCollocations is the mirror: the rule pack
+// recomputes the whole document every run, so a chunk the current text no longer
+// warrants must go — and the coach's flags must stay. Scoping the offline DELETE
+// by type instead of source would have stranded the first row forever.
+func TestOfflinePassReplacesItsOwnCollocations(t *testing.T) {
+	client := &stubClient{response: `{"suggestions":[
+		{"original":"apple","replacement":"an apple","explanation":"article","type":"collocation"}
+	]}`}
+	srv, docID, _ := newTestServer(t, client)
+
+	// A coach flag, then an offline chunk, then a rerun that no longer finds it.
+	do(t, srv, http.MethodPost, "/docs/"+docID+"/collocation", "")
+	postMechanics(t, srv, docID, `[
+		{"from":0,"to":13,"original":"do a decision","replacement":"make a decision","explanation":"pairing","type":"collocation"}
+	]`)
+	got := postMechanics(t, srv, docID, `[]`)
+
+	for _, s := range got {
+		if s.Source == db.SuggestionSourceLocal {
+			t.Errorf("stale offline finding survived a recompute: %+v", s)
+		}
+	}
+	if len(pendingOfType(got, db.SuggestionTypeCollocation)) != 1 {
+		t.Fatalf("the coach's own flag should be untouched, got %+v", got)
+	}
+}
+
+// TestOfflineCollocationPlantsOnAccept closes the loop the family split was for:
+// a chunk the rule pack found, accepted, becomes a vocabulary-garden card — with
+// no model involved anywhere in the path.
+func TestOfflineCollocationPlantsOnAccept(t *testing.T) {
+	srv, docID, h := newTestServer(t, &stubClient{response: `{"suggestions":[]}`})
+	if _, err := h.DB.Exec(
+		`UPDATE documents SET content_text = ? WHERE id = ?`,
+		"I had to do a decision about the job.", docID,
+	); err != nil {
+		t.Fatalf("set content: %v", err)
+	}
+
+	got := postMechanics(t, srv, docID, `[
+		{"from":9,"to":22,"original":"do a decision","replacement":"make a decision","explanation":"pairing","type":"collocation"}
+	]`)
+	if len(got) != 1 {
+		t.Fatalf("want the offline chunk, got %+v", got)
+	}
+	if rec := do(t, srv, http.MethodPost, "/suggestions/"+got[0].ID+"/accept", ""); rec.Code != http.StatusNoContent {
+		t.Fatalf("accept: code=%d body=%s", rec.Code, rec.Body)
+	}
+
+	cards := gardenCards(t, h)
+	if len(cards) != 1 || cards[0].word != "make a decision" {
+		t.Fatalf("want a planted phrase card, got %+v", cards)
+	}
+	// The example is the corrected sentence — the phrasing she kept, not the one
+	// she just left behind.
+	if cards[0].example != "I had to make a decision about the job." {
+		t.Errorf("example should be the corrected sentence, got %q", cards[0].example)
+	}
+}
+
+// TestOfflineCardWinsSpanCollision: the tiebreak is by engine, not by family. An
+// offline miscollocation has an exact span; the coach's overlapping flag is only
+// advisory, so it is the one that goes.
+func TestOfflineCardWinsSpanCollision(t *testing.T) {
+	client := &stubClient{response: `{"suggestions":[
+		{"original":"do a decision about","replacement":"decide about","explanation":"wordy","type":"collocation"}
+	]}`}
+	srv, docID, h := newTestServer(t, client)
+	if _, err := h.DB.Exec(
+		`UPDATE documents SET content_text = ? WHERE id = ?`,
+		"I had to do a decision about the job.", docID,
+	); err != nil {
+		t.Fatalf("set content: %v", err)
+	}
+
+	do(t, srv, http.MethodPost, "/docs/"+docID+"/collocation", "")
+	got := postMechanics(t, srv, docID, `[
+		{"from":9,"to":22,"original":"do a decision","replacement":"make a decision","explanation":"pairing","type":"collocation"}
+	]`)
+
+	if len(got) != 1 {
+		t.Fatalf("want the overlapping coach flag dropped, got %+v", got)
+	}
+	if got[0].Source != db.SuggestionSourceLocal {
+		t.Errorf("the exact offline card should own the span, got %+v", got[0])
+	}
+}