feat(phase4): enrichment — dates->calendar, citations->references, book/paper links

All detection pure/on-device; lookups send only the id/topic (never transcript):
- src/lib/enrich pure modules: dates (absolute + relative, anchored to lectureDate),
  citations (DOI/arXiv/ISBN/author-year), ics (RFC5545), bib (BibTeX/RIS), links
  (legit + Anna's Archive/LibGen search URLs) — 60 tests.
- lookup.ts: CORS-friendly metadata clients (Crossref/OpenAlex/Open Library) +
  Wikipedia summary; AbortController timeouts, session cache, never throws.
- UI: transcript "Dates & references" (add to calendar .ics, look up references +
  open DOI/OpenLibrary/Google Books/Wikipedia/Anna's Archive/LibGen); per-course
  Bibliography screen with BibTeX/RIS export.

Not going to app stores, so Anna's Archive/LibGen links are included per request
(search URLs only — never fetched/proxied). 275 tests green, 0 tsc errors.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/transcript/[id].tsx

@@ -1,3 +1,4 @@
+import * as Linking from 'expo-linking';
 import { Link, Stack, useLocalSearchParams } from 'expo-router';
 import { useEffect, useMemo, useRef, useState } from 'react';
 import {
@@ -16,6 +17,17 @@ import { MaxContentWidth, Spacing } from '@/constants/theme';
 import { useTheme } from '@/hooks/use-theme';
 import { getRepo, type Transcript } from '@/lib/db';
 import { downloadText } from '@/lib/download';
+import {
+  detectCitations,
+  detectEvents,
+  lookupLinksFor,
+  resolveCitation,
+  toIcs,
+  type CandidateEvent,
+  type Citation,
+  type LookupLinks,
+  type RefMetadata,
+} from '@/lib/enrich';
 import { EXPORT_META, formatTranscript, type ExportFormat } from '@/lib/export';
 import { formatClock } from '@/lib/format';
 import {
@@ -54,6 +66,16 @@ export default function TranscriptScreen() {
   const [creatingCards, setCreatingCards] = useState(false);
   const [cardsAdded, setCardsAdded] = useState<number | null>(null);
 
+  // Dates & references (Phase 4) — detected on demand, nothing persisted.
+  // `enrichment === null` means "not scanned yet".
+  const [enrichment, setEnrichment] = useState<{
+    events: CandidateEvent[];
+    citations: Citation[];
+  } | null>(null);
+  // Per-citation resolved metadata + in-flight flags, keyed by list index.
+  const [refMeta, setRefMeta] = useState<Record<number, RefMetadata>>({});
+  const [refLoading, setRefLoading] = useState<Record<number, boolean>>({});
+
   const scrollRef = useRef<ScrollView | null>(null);
   // Y offset of each rendered segment row, captured via onLayout, for scroll-to.
   const segmentYs = useRef<Record<number, number>>({});
@@ -214,6 +236,43 @@ export default function TranscriptScreen() {
     }
   };
 
+  // Scan segments for deadlines + citations. Dates are anchored to the lecture
+  // date when known, else the transcript's creation time. Pure & local.
+  const scanEnrichment = () => {
+    const anchorMs = transcript?.lectureDate ?? transcript?.createdAt ?? Date.now();
+    setEnrichment({
+      events: detectEvents(segments, anchorMs),
+      citations: detectCitations(segments),
+    });
+    setRefMeta({});
+    setRefLoading({});
+  };
+
+  // Download a calendar file for one or more events.
+  const exportIcs = (events: CandidateEvent[]) => {
+    if (events.length === 0) return;
+    const ics = toIcs(
+      events.map((e) => ({ title: e.title, dateMs: e.dateMs, allDay: e.allDay })),
+    );
+    downloadText('event.ics', 'text/calendar', ics);
+  };
+
+  // Network lookup for a single citation (sends only the id string, never text).
+  const lookupRef = async (i: number, c: Citation) => {
+    if (refLoading[i]) return;
+    setRefLoading((prev) => ({ ...prev, [i]: true }));
+    try {
+      const meta = await resolveCitation(c);
+      if (meta) setRefMeta((prev) => ({ ...prev, [i]: meta }));
+    } finally {
+      setRefLoading((prev) => ({ ...prev, [i]: false }));
+    }
+  };
+
+  const openLink = (url: string) => {
+    void Linking.openURL(url);
+  };
+
   if (transcript === undefined) return <Centered><ActivityIndicator /></Centered>;
   if (transcript === null)
     return (
@@ -344,6 +403,129 @@ export default function TranscriptScreen() {
           )}
         </ThemedView>
 
+        {/* Dates & references — detected on demand (pure/local detection). */}
+        <ThemedView type="backgroundElement" style={styles.aidsCard}>
+          <ThemedText type="smallBold">Dates & references</ThemedText>
+          <Pressable
+            onPress={scanEnrichment}
+            disabled={segments.length === 0}
+            style={({ pressed }) => [
+              styles.aidBtn,
+              { backgroundColor: ACCENT, opacity: segments.length === 0 ? 0.5 : pressed ? 0.85 : 1 },
+            ]}>
+            <ThemedText style={styles.aidBtnText}>
+              {enrichment ? 'Re-scan for dates & references' : 'Scan for dates & references'}
+            </ThemedText>
+          </Pressable>
+
+          {enrichment && (
+            <>
+              {/* --- Dates --- */}
+              <View style={styles.aidSection}>
+                <View style={styles.refHeader}>
+                  <ThemedText type="smallBold" themeColor="textSecondary">Dates</ThemedText>
+                  {enrichment.events.length > 0 && (
+                    <Pressable onPress={() => exportIcs(enrichment.events)} hitSlop={6}>
+                      <ThemedText type="linkPrimary">Add all ({enrichment.events.length})</ThemedText>
+                    </Pressable>
+                  )}
+                </View>
+                {enrichment.events.length === 0 ? (
+                  <ThemedText type="small" themeColor="textSecondary">No dates found.</ThemedText>
+                ) : (
+                  enrichment.events.map((e, i) => (
+                    <View key={`evt-${i}`} style={styles.refRow}>
+                      <Pressable
+                        onPress={() => e.start !== undefined && seek(e.start)}
+                        disabled={e.start === undefined}
+                        hitSlop={4}
+                        style={styles.flex}>
+                        <ThemedText type="small">{e.title}</ThemedText>
+                        <ThemedText type="small" themeColor="textSecondary">
+                          {formatEventDate(e)}
+                          {e.start !== undefined ? ` · ${formatClock(e.start)}` : ''}
+                        </ThemedText>
+                      </Pressable>
+                      <Pressable onPress={() => exportIcs([e])} hitSlop={6}>
+                        <ThemedText type="link" themeColor="textSecondary">Add to calendar</ThemedText>
+                      </Pressable>
+                    </View>
+                  ))
+                )}
+              </View>
+
+              {/* --- References --- */}
+              <View style={styles.aidSection}>
+                <ThemedText type="smallBold" themeColor="textSecondary">References</ThemedText>
+                {enrichment.citations.length === 0 ? (
+                  <ThemedText type="small" themeColor="textSecondary">No references found.</ThemedText>
+                ) : (
+                  enrichment.citations.map((c, i) => {
+                    const meta = refMeta[i];
+                    const links = lookupLinksFor(c, meta);
+                    return (
+                      <View key={`cit-${i}`} style={styles.citCard}>
+                        <View style={styles.refRow}>
+                          <Pressable
+                            onPress={() => c.start !== undefined && seek(c.start)}
+                            disabled={c.start === undefined}
+                            hitSlop={4}
+                            style={styles.flex}>
+                            <ThemedText type="small">{c.raw}</ThemedText>
+                            {c.start !== undefined && (
+                              <ThemedText type="code" themeColor="textSecondary">
+                                {formatClock(c.start)}
+                              </ThemedText>
+                            )}
+                          </Pressable>
+                          <Pressable
+                            onPress={() => void lookupRef(i, c)}
+                            disabled={refLoading[i]}
+                            hitSlop={6}>
+                            {refLoading[i] ? (
+                              <ActivityIndicator size="small" />
+                            ) : (
+                              <ThemedText type="link" themeColor="textSecondary">
+                                {meta ? 'Looked up' : 'Look up'}
+                              </ThemedText>
+                            )}
+                          </Pressable>
+                        </View>
+
+                        {meta && (
+                          <View style={styles.metaBox}>
+                            {meta.title && <ThemedText type="smallBold">{meta.title}</ThemedText>}
+                            {(meta.authors?.length || meta.year) && (
+                              <ThemedText type="small" themeColor="textSecondary">
+                                {[meta.authors?.join(', '), meta.year].filter(Boolean).join(' · ')}
+                              </ThemedText>
+                            )}
+                            <ThemedText type="small" themeColor="textSecondary">{meta.source}</ThemedText>
+                          </View>
+                        )}
+
+                        <View style={styles.linkChips}>
+                          {linkEntries(links).map(([label, url]) => (
+                            <Pressable
+                              key={label}
+                              onPress={() => openLink(url)}
+                              style={({ pressed }) => [
+                                styles.linkChip,
+                                { backgroundColor: theme.backgroundSelected, opacity: pressed ? 0.7 : 1 },
+                              ]}>
+                              <ThemedText type="small">{label}</ThemedText>
+                            </Pressable>
+                          ))}
+                        </View>
+                      </View>
+                    );
+                  })
+                )}
+              </View>
+            </>
+          )}
+        </ThemedView>
+
         {segments.map((s, i) => (
           <View
             key={i}
@@ -404,6 +586,32 @@ function Centered({ children }: { children: React.ReactNode }) {
   return <ThemedView style={[styles.fill, styles.centered]}>{children}</ThemedView>;
 }
 
+/** Localized date for a candidate event — date-only when it's an all-day item. */
+function formatEventDate(e: CandidateEvent): string {
+  const d = new Date(e.dateMs);
+  return e.allDay
+    ? d.toLocaleDateString()
+    : d.toLocaleString([], { dateStyle: 'medium', timeStyle: 'short' });
+}
+
+/** Ordered, labeled, defined link entries from a LookupLinks bag. */
+function linkEntries(links: LookupLinks): [string, string][] {
+  const order: [keyof LookupLinks, string][] = [
+    ['doi', 'DOI'],
+    ['arxiv', 'arXiv'],
+    ['openAlex', 'OpenAlex'],
+    ['openLibrary', 'Open Library'],
+    ['googleBooks', 'Google Books'],
+    ['wikipedia', 'Wikipedia'],
+    ['annasArchive', "Anna's Archive"],
+    ['libgen', 'LibGen'],
+  ];
+  return order
+    .map(([key, label]) => [label, links[key]] as const)
+    .filter((pair): pair is [string, string] => typeof pair[1] === 'string' && pair[1].length > 0)
+    .map(([label, url]) => [label, url]);
+}
+
 const styles = StyleSheet.create({
   fill: { flex: 1 },
   centered: { alignItems: 'center', justifyContent: 'center' },
@@ -419,6 +627,12 @@ const styles = StyleSheet.create({
   aidSection: { gap: Spacing.one, marginTop: Spacing.one },
   aidLine: { flexDirection: 'row', gap: Spacing.two, alignItems: 'flex-start', paddingVertical: 2 },
   flex: { flex: 1 },
+  refHeader: { flexDirection: 'row', alignItems: 'center', justifyContent: 'space-between', gap: Spacing.two },
+  refRow: { flexDirection: 'row', gap: Spacing.two, alignItems: 'flex-start', paddingVertical: 2 },
+  citCard: { gap: Spacing.one, paddingVertical: Spacing.one },
+  metaBox: { gap: 2, paddingLeft: Spacing.two },
+  linkChips: { flexDirection: 'row', flexWrap: 'wrap', gap: Spacing.one },
+  linkChip: { paddingHorizontal: Spacing.two, paddingVertical: 2, borderRadius: 999 },
   segRow: { flexDirection: 'row', gap: Spacing.two, paddingVertical: Spacing.one, paddingHorizontal: Spacing.two, borderRadius: Spacing.two, alignItems: 'flex-start' },
   ts: { paddingTop: 4, minWidth: 52 },
   segText: { flex: 1, fontSize: 16, lineHeight: 24, padding: 0 },