diff --git a/.abcd/development/brief/04-surfaces/01-demo.md b/.abcd/development/brief/04-surfaces/01-demo.md
index 9149181..7f17002 100644
--- a/.abcd/development/brief/04-surfaces/01-demo.md
+++ b/.abcd/development/brief/04-surfaces/01-demo.md
@@ -25,7 +25,9 @@ app contains at least one intentional usability flaw, found by talking.
   array of raw rrweb events, one per line, to `events.rrweb.jsonl`. Request
   bodies are validated as JSON, re-encoded to a single line so an embedded
   newline cannot split one record across lines, and size-limited (8 MiB);
-  writes are serialised under a mutex.
+  writes are serialised under a mutex. A persisted batch answers `204 No
+  Content`; if an append fails the endpoint answers `500` rather than a false
+  `204`, so the client does not treat a dropped event as captured.
 - The capture surface is loopback-only by default and the write endpoints are
   guarded against cross-origin forgery: a request must carry a loopback `Host`,
   a same-origin (or absent) `Origin`, and `Content-Type: application/json`.
diff --git a/.abcd/development/brief/04-surfaces/03-merge.md b/.abcd/development/brief/04-surfaces/03-merge.md
index 46ab5a4..c83af16 100644
--- a/.abcd/development/brief/04-surfaces/03-merge.md
+++ b/.abcd/development/brief/04-surfaces/03-merge.md
@@ -13,8 +13,12 @@ alongside the manifest.
 
 ## Behaviour
 
-- Reads `manifest.json`, `transcript.jsonl`, and `interactions.jsonl`; a
-  missing file is an error.
+- Reads `manifest.json` (required), `transcript.jsonl`, and
+  `interactions.jsonl`. A missing `transcript.jsonl` or `interactions.jsonl` is
+  treated as zero records, not an error, so a default audio-only `record`
+  session (which never writes `interactions.jsonl`) still merges to a
+  speech-only timeline, and a session merged before transcription still merges
+  to an event-only one. A malformed line in either file is still an error.
 - Utterances enter as `src: "speech"` entries at their `t0` (already
   session-relative); interactions enter as `src: "event"` entries with epoch
   milliseconds converted via `t0_epoch_ms`, and are assigned sequential
diff --git a/.abcd/development/brief/05-internals/02-schemas.md b/.abcd/development/brief/05-internals/02-schemas.md
index 4ed4a73..e743a27 100644
--- a/.abcd/development/brief/05-internals/02-schemas.md
+++ b/.abcd/development/brief/05-internals/02-schemas.md
@@ -120,5 +120,9 @@ validation boundary; every field below is checked, and `status` is forced to
 ```
 
 Effective status: every finding starts `unverified`; verdict records apply in
-file order and the last one for a finding wins. Design and rationale:
+file order and the last one for a finding wins. A verdict whose `verdict` value
+is outside the closed enum (a typo, an empty string, or a foreign value in a
+shared session) is ignored, so its finding keeps `unverified` and still appears
+in the report and review queue rather than vanishing into an unrendered group.
+Design and rationale:
 [`../01-product/04-analysis.md`](../01-product/04-analysis.md).
diff --git a/.abcd/work/DECISIONS.md b/.abcd/work/DECISIONS.md
index 0f9885e..7e32908 100644
--- a/.abcd/work/DECISIONS.md
+++ b/.abcd/work/DECISIONS.md
@@ -128,3 +128,22 @@ Architecture-shaping decisions graduate to an ADR under
   alone and prints that installing `gh` enables provenance verification. The
   dependency section (ffmpeg pinned-GPG path, whisperx/whisper.cpp, private-mktemp
   uv install) is unchanged.
+- 2026-07-18 — bughunt-1 correctness fixes. `timeline.Merge` now treats a
+  missing `transcript.jsonl`/`interactions.jsonl` as zero records (via
+  `readOptionalJSONL`, tolerating `fs.ErrNotExist`), so the documented default
+  audio-only `record` → `merge` pipeline no longer aborts with "no such file";
+  brief 04-surfaces/03-merge.md and docs/reference/cli.md updated.
+- 2026-07-18 — Demo capture handler (`appendLines`) now checks the append
+  write error and answers `500` instead of a false `204`, and writes each
+  record + newline as one buffer so a partial write cannot leave a truncated,
+  unparseable JSONL line; brief 04-surfaces/01-demo.md updated.
+- 2026-07-18 — `analyze.Load` validates the verdict enum (the previously-unused
+  `verdictSet`): a verdict value outside `confirmed|rejected|duplicate` is
+  ignored, so its finding stays `unverified` and no longer vanishes from the
+  report and review queue into an unrendered status group; schema doc noted.
+- 2026-07-18 — `session.WriteJSONL` and `review.AppendVerdict` now return the
+  file `Close()` error (matching `WriteFileNoFollow`), so a write-back failure
+  deferred to close is not masked as success on committed artefacts.
+- 2026-07-18 — Demo/record banners derive the display URL via `demo.DisplayURL`
+  instead of concatenating `-addr` after a literal "localhost", fixing the
+  broken `http://localhost0.0.0.0:8737` shown for an explicit-host bind.
diff --git a/docs/reference/cli.md b/docs/reference/cli.md
index 45a37c6..054db70 100644
--- a/docs/reference/cli.md
+++ b/docs/reference/cli.md
@@ -72,7 +72,7 @@ testimony merge -session DIR
 |---|---|---|
 | `-session` | *(required)* | session directory |
 
-Behaviour: reads `manifest.json`, `transcript.jsonl`, and `interactions.jsonl`; converts interaction epoch-millisecond times to session-relative seconds via `t0_epoch_ms`; writes the time-sorted `timeline.jsonl`; prints `merged N utterances + M events → <path>`.
+Behaviour: reads `manifest.json` (required), `transcript.jsonl`, and `interactions.jsonl`; converts interaction epoch-millisecond times to session-relative seconds via `t0_epoch_ms`; writes the time-sorted `timeline.jsonl`; prints `merged N utterances + M events → <path>`. A missing `transcript.jsonl` or `interactions.jsonl` counts as zero records rather than an error, so a default audio-only `record` session (which never writes `interactions.jsonl`) still merges to a speech-only timeline.
 
 ## `testimony report`
 
diff --git a/internal/analyze/analyze.go b/internal/analyze/analyze.go
index 45e0e5a..85429df 100644
--- a/internal/analyze/analyze.go
+++ b/internal/analyze/analyze.go
@@ -112,6 +112,16 @@ func Load(dir string) ([]Finding, []Verdict, error) {
 			if err := json.Unmarshal(raw, &v); err != nil {
 				return nil, nil, fmt.Errorf("%s:%d: %w", path, line, err)
 			}
+			// The verdict enum is closed (confirmed|rejected|duplicate). A verdict
+			// carrying any other value — a typo, an empty string, or a foreign
+			// value from a shared/hand-edited session — is not representable, so it
+			// is ignored rather than applied. The finding then keeps its
+			// "unverified" status and still appears in the report and the review
+			// queue, instead of landing in a status group nothing renders and
+			// silently vanishing from both.
+			if !verdictSet[v.Verdict] {
+				continue
+			}
 			verdicts = append(verdicts, v)
 			continue
 		}
diff --git a/internal/demo/demo.go b/internal/demo/demo.go
index 02ce647..209f600 100644
--- a/internal/demo/demo.go
+++ b/internal/demo/demo.go
@@ -60,7 +60,7 @@ func Run(addr, outRoot string) error {
 	fmt.Printf(`testimony demo — capture session started
 
   session dir : %s
-  url         : http://localhost%s
+  url         : %s
 
   1. Start your voice/screen recorder NOW (QuickTime → File → New Audio Recording).
   2. Say “session start” aloud, open the URL, and think aloud while you explore.
@@ -70,7 +70,7 @@ func Run(addr, outRoot string) error {
        testimony merge      -session %s
        testimony report     -session %s
 
-`, dir, addr, dir, dir, dir)
+`, dir, DisplayURL(addr), dir, dir, dir)
 
 	// Block until interrupted, then shut the server down cleanly.
 	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
@@ -175,8 +175,17 @@ func (s *server) appendLines(w http.ResponseWriter, r *http.Request, f *os.File,
 	s.mu.Lock()
 	defer s.mu.Unlock()
 	for _, l := range lines {
-		f.Write(l)
-		f.Write([]byte("\n"))
+		// Write the record and its terminating newline as a single buffer: a
+		// partial write (e.g. ENOSPC) can then never land a data line without
+		// its newline, which would join to the next successful write and produce
+		// one malformed physical line that later fails merge's JSONL reader.
+		if _, err := f.Write(append(l, '\n')); err != nil {
+			// The capture was not persisted; tell the client so it does not treat
+			// a dropped event as recorded, rather than answering 204 as if it had
+			// succeeded.
+			http.Error(w, "capture write failed", http.StatusInternalServerError)
+			return
+		}
 	}
 	w.WriteHeader(http.StatusNoContent)
 }
@@ -249,6 +258,24 @@ func isJSONContentType(ct string) bool {
 // are not published to the LAN even though the banner prints "localhost". An
 // operator who deliberately wants a wider bind can still pass an explicit host
 // (e.g. "0.0.0.0:8737").
+// DisplayURL renders the human-facing URL an operator opens for a capture
+// server bound to addr. It shows "localhost" only for the host-less default
+// (":8737" -> http://localhost:8737); when an operator passes an explicit host
+// for a wider bind (e.g. "0.0.0.0:8737") it shows that host, so the printed URL
+// is never the broken "http://localhost0.0.0.0:8737" that raw concatenation of
+// addr after the "localhost" literal produced. Shared by demo.Run and
+// record.printStatus.
+func DisplayURL(addr string) string {
+	host, port, err := net.SplitHostPort(addr)
+	if err != nil {
+		return "http://localhost" + addr // malformed addr: preserve the old form
+	}
+	if host == "" {
+		host = "localhost"
+	}
+	return "http://" + net.JoinHostPort(host, port)
+}
+
 func listenAddr(addr string) string {
 	host, port, err := net.SplitHostPort(addr)
 	if err != nil {
diff --git a/internal/demo/demo_test.go b/internal/demo/demo_test.go
index 18c9105..7d92e73 100644
--- a/internal/demo/demo_test.go
+++ b/internal/demo/demo_test.go
@@ -125,6 +125,44 @@ func TestBatchCompactsEmbeddedNewline(t *testing.T) {
 	}
 }
 
+// TestAppendLinesReportsWriteError is the dropped-write regression: when the
+// append to a stream file fails, the handler must not answer 204 (which tells the
+// browser the capture was persisted and stops it re-sending). Here the stream
+// file is closed underneath the server so its Write fails; the handler must
+// surface an error status instead of a silent 204.
+func TestAppendLinesReportsWriteError(t *testing.T) {
+	s, _ := newTestServer(t)
+	if err := s.interactions.Close(); err != nil {
+		t.Fatalf("close: %v", err)
+	}
+
+	w := httptest.NewRecorder()
+	s.handleInteraction(w, jsonPost("/api/interactions", "{\"t\":1,\"kind\":\"click\"}", nil))
+	if w.Code == http.StatusNoContent {
+		t.Fatalf("a failed capture write returned 204; want an error status")
+	}
+	if w.Code != http.StatusInternalServerError {
+		t.Fatalf("status = %d, want 500", w.Code)
+	}
+}
+
+// TestDisplayURL pins the human-facing URL: "localhost" only for the host-less
+// default, and the real host otherwise, never the broken "localhost0.0.0.0:8737"
+// that concatenating a full -addr after the "localhost" literal produced.
+func TestDisplayURL(t *testing.T) {
+	cases := map[string]string{
+		":8737":          "http://localhost:8737",
+		"0.0.0.0:8737":   "http://0.0.0.0:8737",
+		"127.0.0.1:8737": "http://127.0.0.1:8737",
+		"[::1]:8737":     "http://[::1]:8737",
+	}
+	for in, want := range cases {
+		if got := DisplayURL(in); got != want {
+			t.Errorf("DisplayURL(%q) = %q, want %q", in, got, want)
+		}
+	}
+}
+
 // TestWriteEndpointGuard covers the CSRF / DNS-rebinding surface: a request must
 // carry a JSON Content-Type, a loopback Host, and (when present) a same-origin
 // Origin. A rejected request must write nothing.
diff --git a/internal/record/record.go b/internal/record/record.go
index 16e26d2..3880870 100644
--- a/internal/record/record.go
+++ b/internal/record/record.go
@@ -285,7 +285,7 @@ func printStatus(log io.Writer, recorders []string, demoOn bool, addr string) {
 		fmt.Fprintf(log, "  recording   : %s\n", strings.Join(recorders, ", "))
 	}
 	if demoOn {
-		fmt.Fprintf(log, "  demo url    : http://localhost%s\n", addr)
+		fmt.Fprintf(log, "  demo url    : %s\n", demo.DisplayURL(addr))
 	}
 	fmt.Fprint(log, "\n  Say “session start” aloud, then think aloud while you work.\n")
 	fmt.Fprint(log, "  Press Ctrl+C to stop.\n")
diff --git a/internal/report/report_test.go b/internal/report/report_test.go
index 3a438e4..27437a2 100644
--- a/internal/report/report_test.go
+++ b/internal/report/report_test.go
@@ -88,6 +88,37 @@ func TestReportNoFindings(t *testing.T) {
 	}
 }
 
+// TestReportKeepsFindingWithUnknownVerdict is the vanishing-finding regression.
+// findings.jsonl is a shared/hand-editable artefact; a verdict line carrying a
+// value outside the closed enum (here a "confirm" typo) must not push its finding
+// into an unrendered status group. The finding must still appear, falling back to
+// Unverified, rather than disappearing from the report entirely.
+func TestReportKeepsFindingWithUnknownVerdict(t *testing.T) {
+	dir := t.TempDir()
+	if err := session.SaveManifest(dir, session.Manifest{Session: "fixture", App: "app", Participant: "P1"}); err != nil {
+		t.Fatalf("SaveManifest: %v", err)
+	}
+	if err := os.WriteFile(filepath.Join(dir, session.TimelineFile), []byte(timelineFixture), 0o644); err != nil {
+		t.Fatalf("write timeline: %v", err)
+	}
+	findings := "{\"id\":\"F-001\",\"t\":22,\"type\":\"bug\",\"severity\":3,\"quote\":\"ok\",\"evidence\":[\"utt-004\"],\"status\":\"unverified\"}\n" +
+		"{\"kind\":\"verdict\",\"finding\":\"F-001\",\"verdict\":\"confirm\",\"at\":\"2026-07-17\"}\n"
+	if err := os.WriteFile(filepath.Join(dir, session.FindingsFile), []byte(findings), 0o644); err != nil {
+		t.Fatalf("write findings: %v", err)
+	}
+
+	md, err := Render(dir, 2.5)
+	if err != nil {
+		t.Fatalf("Render: %v", err)
+	}
+	if !strings.Contains(md, "**F-001**") {
+		t.Fatalf("finding with an unrecognised verdict vanished from the report:\n%s", md)
+	}
+	if !strings.Contains(md, "### Unverified (1)") {
+		t.Fatalf("finding with an unrecognised verdict should fall back to Unverified:\n%s", md)
+	}
+}
+
 func findingLines(t *testing.T, dir string) []string {
 	t.Helper()
 	b, err := os.ReadFile(filepath.Join(dir, session.FindingsFile))
diff --git a/internal/review/review.go b/internal/review/review.go
index 0893414..267385c 100644
--- a/internal/review/review.go
+++ b/internal/review/review.go
@@ -210,11 +210,13 @@ func AppendVerdict(dir string, v analyze.Verdict) error {
 	if err != nil {
 		return err
 	}
-	defer f.Close()
 	if _, err := f.Write(append(b, '\n')); err != nil {
+		f.Close()
 		return err
 	}
-	return nil
+	// Return the Close error so a verdict is never reported recorded when its
+	// bytes did not reach disk (write-back deferred to close on NFS/full device).
+	return f.Close()
 }
 
 // printFinding writes a finding to the analyst's terminal. Every
diff --git a/internal/session/session.go b/internal/session/session.go
index 8260756..4b5a9ed 100644
--- a/internal/session/session.go
+++ b/internal/session/session.go
@@ -197,14 +197,22 @@ func WriteJSONL[T any](path string, values []T) error {
 	if err != nil {
 		return err
 	}
-	defer f.Close()
 
 	w := bufio.NewWriter(f)
 	enc := json.NewEncoder(w)
 	for _, v := range values {
 		if err := enc.Encode(v); err != nil {
+			f.Close()
 			return err
 		}
 	}
-	return w.Flush()
+	if err := w.Flush(); err != nil {
+		f.Close()
+		return err
+	}
+	// Return the Close error: on a filesystem that defers write-back errors to
+	// close (NFS close-to-open, or a full device), the final failure surfaces
+	// here, not from Flush — mirroring WriteFileNoFollow, so a committed artefact
+	// is never reported written when its bytes did not reach disk.
+	return f.Close()
 }
diff --git a/internal/timeline/timeline.go b/internal/timeline/timeline.go
index 327967a..2ac43f1 100644
--- a/internal/timeline/timeline.go
+++ b/internal/timeline/timeline.go
@@ -4,7 +4,9 @@
 package timeline
 
 import (
+	"errors"
 	"fmt"
+	"io/fs"
 	"path/filepath"
 	"sort"
 
@@ -123,6 +125,21 @@ func EventsNear(entries []Entry, u Entry, window float64) []string {
 	return ids
 }
 
+// readOptionalJSONL reads a JSONL input that a valid session may legitimately
+// lack. A default audio-only `testimony record` run captures no interactions,
+// and a session may equally reach merge before transcription: an absent file is
+// therefore zero records, not a fatal error, so an audio-only or interaction-only
+// session still merges to a partial timeline instead of aborting the documented
+// pipeline. Any other read error (a malformed line, a permission failure) is
+// still returned unchanged.
+func readOptionalJSONL[T any](path string) ([]T, error) {
+	out, err := session.ReadJSONL[T](path)
+	if errors.Is(err, fs.ErrNotExist) {
+		return nil, nil
+	}
+	return out, err
+}
+
 // Merge reads manifest, transcript and interactions from dir, writes
 // timeline.jsonl, and returns the number of speech and event entries.
 func Merge(dir string) (speech, events int, err error) {
@@ -130,11 +147,11 @@ func Merge(dir string) (speech, events int, err error) {
 	if err != nil {
 		return 0, 0, err
 	}
-	utts, err := session.ReadJSONL[Utterance](filepath.Join(dir, session.TranscriptFile))
+	utts, err := readOptionalJSONL[Utterance](filepath.Join(dir, session.TranscriptFile))
 	if err != nil {
 		return 0, 0, fmt.Errorf("read transcript: %w", err)
 	}
-	ints, err := session.ReadJSONL[Interaction](filepath.Join(dir, session.InteractionsFile))
+	ints, err := readOptionalJSONL[Interaction](filepath.Join(dir, session.InteractionsFile))
 	if err != nil {
 		return 0, 0, fmt.Errorf("read interactions: %w", err)
 	}
diff --git a/internal/timeline/timeline_test.go b/internal/timeline/timeline_test.go
index 3ea64c6..80e2d65 100644
--- a/internal/timeline/timeline_test.go
+++ b/internal/timeline/timeline_test.go
@@ -1,6 +1,12 @@
 package timeline
 
-import "testing"
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/REPPL/Testimony/internal/session"
+)
 
 const t0 = int64(1_784_300_400_000) // arbitrary session anchor, epoch ms
 
@@ -41,6 +47,33 @@ func TestBuildEntriesSortsByTime(t *testing.T) {
 	}
 }
 
+// TestMergeAudioOnlySession is the audio-only-record regression: a default
+// `testimony record` session has manifest + transcript but no interactions.jsonl
+// (only the demo server writes that file), and record itself prints `merge` as
+// the next step. Merge must treat the absent interactions file as zero events and
+// still write a speech-only timeline, not abort with a "no such file" error.
+func TestMergeAudioOnlySession(t *testing.T) {
+	dir := t.TempDir()
+	if err := session.SaveManifest(dir, session.Manifest{Session: "s", T0EpochMS: t0}); err != nil {
+		t.Fatalf("SaveManifest: %v", err)
+	}
+	utts := []Utterance{{ID: "utt-001", T0: 1, T1: 2, Speaker: "P1", Text: "hello"}}
+	if err := session.WriteJSONL(filepath.Join(dir, session.TranscriptFile), utts); err != nil {
+		t.Fatalf("write transcript: %v", err)
+	}
+
+	speech, events, err := Merge(dir)
+	if err != nil {
+		t.Fatalf("Merge on audio-only session: %v", err)
+	}
+	if speech != 1 || events != 0 {
+		t.Fatalf("want speech=1 events=0, got speech=%d events=%d", speech, events)
+	}
+	if _, err := os.Stat(filepath.Join(dir, session.TimelineFile)); err != nil {
+		t.Fatalf("timeline.jsonl not written: %v", err)
+	}
+}
+
 func TestEventsNearWindow(t *testing.T) {
 	entries := sample()
 	var speech []Entry