package agent

import (
	"errors"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"testing"
	"time"

	"reasonix/internal/provider"
	"reasonix/internal/store"
)

func sessionWithTurns(t *testing.T, path string, turns int) *Session {
	t.Helper()
	s := NewSession("sys")
	for i := range turns {
		s.Add(provider.Message{Role: provider.RoleUser, Content: "prompt " + strings.Repeat("x", 8)})
		s.Add(provider.Message{Role: provider.RoleAssistant, Content: "reply"})
		if err := s.SaveSnapshot(path); err != nil {
			t.Fatalf("SaveSnapshot turn %d: %v", i, err)
		}
	}
	return s
}

func TestLoadSessionToleratesTornEventLogTail(t *testing.T) {
	path := filepath.Join(t.TempDir(), "session.jsonl")
	s := sessionWithTurns(t, path, 2)
	want := len(s.Snapshot())

	logPath := store.SessionEventLog(path)
	f, err := os.OpenFile(logPath, os.O_WRONLY|os.O_APPEND, 0o644)
	if err != nil {
		t.Fatalf("open log: %v", err)
	}
	if _, err := f.Write([]byte(`{"schema_version":1,"type":"append","message_index":5,"mess`)); err != nil {
		t.Fatalf("write torn tail: %v", err)
	}
	f.Close()

	loaded, err := LoadSession(path)
	if err != nil {
		t.Fatalf("LoadSession with torn tail: %v", err)
	}
	if len(loaded.Messages) != want {
		t.Fatalf("messages with torn tail = %d, want %d", len(loaded.Messages), want)
	}
	if !loaded.eventLogDamaged {
		t.Fatal("eventLogDamaged = false, want true for torn tail")
	}
}

func TestSaveSnapshotHealsTornEventLogTail(t *testing.T) {
	path := filepath.Join(t.TempDir(), "session.jsonl")
	sessionWithTurns(t, path, 2)

	logPath := store.SessionEventLog(path)
	intact, err := os.ReadFile(logPath)
	if err != nil {
		t.Fatalf("read log: %v", err)
	}
	if err := os.WriteFile(logPath, append(intact, []byte(`{"schema_version":1,"type":"ap`)...), 0o644); err != nil {
		t.Fatalf("write torn log: %v", err)
	}

	// A fresh runtime resumes the session and keeps chatting: the save must
	// truncate the torn tail (not bury it) and the appended turn must replay.
	resumed, err := LoadSession(path)
	if err != nil {
		t.Fatalf("LoadSession: %v", err)
	}
	resumed.Add(provider.Message{Role: provider.RoleUser, Content: "after crash"})
	if err := resumed.SaveSnapshot(path); err != nil {
		t.Fatalf("SaveSnapshot after torn tail: %v", err)
	}

	reloaded, err := LoadSession(path)
	if err != nil {
		t.Fatalf("LoadSession after heal: %v", err)
	}
	if reloaded.eventLogDamaged {
		t.Fatal("event log still damaged after healing save")
	}
	tail := reloaded.Messages[len(reloaded.Messages)-1]
	if tail.Content != "after crash" {
		t.Fatalf("healed tail = %q, want %q", tail.Content, "after crash")
	}
}

func TestLoadSessionIgnoresForeignEventLog(t *testing.T) {
	path := filepath.Join(t.TempDir(), "session.jsonl")
	sessionWithTurns(t, path, 1)

	// A file this build cannot own squats the native log path: undecodable
	// bytes, or a legacy v0.x Claude-style event transcript left in place by
	// migration. It must be read-ignored and never written to.
	logPath := store.SessionEventLog(path)
	foreign := "garbage that is not json\n"
	if err := os.WriteFile(logPath, []byte(foreign), 0o644); err != nil {
		t.Fatalf("write foreign log: %v", err)
	}

	loaded, err := LoadSession(path)
	if err != nil {
		t.Fatalf("LoadSession with foreign log: %v", err)
	}
	if len(loaded.Messages) == 0 {
		t.Fatal("expected checkpoint transcript, got empty session")
	}
	if loaded.eventLogDamaged {
		t.Fatal("foreign log misreported as damaged native log")
	}

	// Saves keep working checkpoint-only and never touch the foreign file.
	loaded.Add(provider.Message{Role: provider.RoleUser, Content: "still works"})
	if err := loaded.SaveSnapshot(path); err != nil {
		t.Fatalf("SaveSnapshot with foreign log: %v", err)
	}
	got, err := os.ReadFile(logPath)
	if err != nil {
		t.Fatalf("read foreign log: %v", err)
	}
	if string(got) != foreign {
		t.Fatalf("foreign log was modified:\nbefore=%q\nafter=%q", foreign, got)
	}
	reloaded, err := LoadSession(path)
	if err != nil {
		t.Fatalf("LoadSession after checkpoint-only save: %v", err)
	}
	if got := reloaded.Messages[len(reloaded.Messages)-1].Content; got != "still works" {
		t.Fatalf("checkpoint-only tail = %q, want %q", got, "still works")
	}
}

func TestSaveLeavesLegacyEventTranscriptUntouched(t *testing.T) {
	// The v0.x migration reconstructs sessions from legacy Claude-style
	// ".events.jsonl" transcripts that live in the SAME directory the native
	// session is imported into — i.e. exactly at the native event-log path.
	// The import must succeed, and the user's original file must survive
	// byte-for-byte.
	dir := t.TempDir()
	path := filepath.Join(dir, "chat-1.jsonl")
	legacy := `{"type":"user.message","id":1,"ts":"t","turn":0,"text":"hello from v0.x"}` + "\n" +
		`{"type":"model.final","id":2,"ts":"t","turn":0,"content":"hi","toolCalls":[],"usage":{},"costUsd":0}` + "\n"
	logPath := store.SessionEventLog(path)
	if err := os.WriteFile(logPath, []byte(legacy), 0o644); err != nil {
		t.Fatalf("write legacy transcript: %v", err)
	}

	s := NewSession("")
	s.Add(provider.Message{Role: provider.RoleUser, Content: "hello from v0.x"})
	s.Add(provider.Message{Role: provider.RoleAssistant, Content: "hi"})
	if err := s.Save(path); err != nil {
		t.Fatalf("Save beside legacy transcript: %v", err)
	}

	got, err := os.ReadFile(logPath)
	if err != nil {
		t.Fatalf("read legacy transcript: %v", err)
	}
	if string(got) != legacy {
		t.Fatalf("legacy transcript modified:\nbefore=%q\nafter=%q", legacy, got)
	}
	loaded, err := LoadSession(path)
	if err != nil {
		t.Fatalf("LoadSession of imported session: %v", err)
	}
	if len(loaded.Messages) != 2 || loaded.Messages[1].Content != "hi" {
		t.Fatalf("imported transcript = %+v", loaded.Messages)
	}
}

// TestRepairPreservesDamagedTailBytes locks in the #6607 content-loss fix:
// bytes the tail repair truncates away — including intact turns buried behind
// an out-of-order record, the dual-writer shape — must be salvaged to the
// .damaged sidecar instead of discarded forever.
func TestRepairPreservesDamagedTailBytes(t *testing.T) {
	path := filepath.Join(t.TempDir(), "session.jsonl")
	sessionWithTurns(t, path, 2)

	logPath := store.SessionEventLog(path)
	// An out-of-order append (as an interleaving second writer would leave)
	// followed by a torn partial record: replay stops before both, and repair
	// truncates both away.
	buried := `{"schema_version":1,"type":"append","message_index":99,"messages":[{"role":"user","content":"buried turn"}],"created_at":"2026-01-01T00:00:00Z"}` + "\n"
	torn := `{"schema_version":1,"type":"ap`
	f, err := os.OpenFile(logPath, os.O_WRONLY|os.O_APPEND, 0o644)
	if err != nil {
		t.Fatalf("open log: %v", err)
	}
	if _, err := f.Write([]byte(buried + torn)); err != nil {
		t.Fatalf("write damaged tail: %v", err)
	}
	f.Close()

	// The healing save truncates the tail; preservation must run first.
	resumed, err := LoadSession(path)
	if err != nil {
		t.Fatalf("LoadSession: %v", err)
	}
	resumed.Add(provider.Message{Role: provider.RoleUser, Content: "after damage"})
	if err := resumed.SaveSnapshot(path); err != nil {
		t.Fatalf("SaveSnapshot after damage: %v", err)
	}

	salvaged, err := os.ReadFile(store.SessionEventLogDamaged(path))
	if err != nil {
		t.Fatalf("read damaged sidecar: %v", err)
	}
	if !strings.Contains(string(salvaged), "buried turn") {
		t.Fatalf("salvage sidecar is missing the buried turn:\n%s", salvaged)
	}
	if !strings.Contains(string(salvaged), `"damaged_tail":true`) {
		t.Fatalf("salvage sidecar is missing the incident header:\n%s", salvaged)
	}
	// The log itself must be healed: replay to the end, no damage, and the
	// buried record must not leak back into the transcript.
	reloaded, err := LoadSession(path)
	if err != nil {
		t.Fatalf("LoadSession after heal: %v", err)
	}
	if reloaded.eventLogDamaged {
		t.Fatal("event log still damaged after healing save")
	}
	for _, m := range reloaded.Messages {
		if m.Content == "buried turn" {
			t.Fatal("truncated record leaked back into the transcript")
		}
	}

	// A second incident appends to the sidecar instead of overwriting the
	// first salvage.
	f, err = os.OpenFile(store.SessionEventLog(path), os.O_WRONLY|os.O_APPEND, 0o644)
	if err != nil {
		t.Fatalf("reopen log: %v", err)
	}
	if _, err := f.Write([]byte(`{"schema_version":1,"type":"append","message_index":77,"messages":[{"role":"user","content":"second incident"}],"created_at":"2026-01-01T00:00:00Z"}` + "\n")); err != nil {
		t.Fatalf("write second damage: %v", err)
	}
	f.Close()
	resumed2, err := LoadSession(path)
	if err != nil {
		t.Fatalf("LoadSession second incident: %v", err)
	}
	resumed2.Add(provider.Message{Role: provider.RoleUser, Content: "after second"})
	if err := resumed2.SaveSnapshot(path); err != nil {
		t.Fatalf("SaveSnapshot second incident: %v", err)
	}
	salvaged, err = os.ReadFile(store.SessionEventLogDamaged(path))
	if err != nil {
		t.Fatalf("read damaged sidecar after second incident: %v", err)
	}
	if !strings.Contains(string(salvaged), "buried turn") || !strings.Contains(string(salvaged), "second incident") {
		t.Fatalf("salvage sidecar must keep both incidents:\n%s", salvaged)
	}
}

func TestReplayStopsAtBrokenAppendChain(t *testing.T) {
	path := filepath.Join(t.TempDir(), "session.jsonl")
	sessionWithTurns(t, path, 1)
	logPath := store.SessionEventLog(path)
	// Append an event whose MessageIndex does not chain onto the transcript.
	f, err := os.OpenFile(logPath, os.O_WRONLY|os.O_APPEND, 0o644)
	if err != nil {
		t.Fatalf("open log: %v", err)
	}
	if _, err := f.Write([]byte(`{"schema_version":1,"type":"append","message_index":99,"messages":[{"role":"user","content":"lost"}],"created_at":"2026-01-01T00:00:00Z"}` + "\n")); err != nil {
		t.Fatalf("write broken chain: %v", err)
	}
	f.Close()

	replay, err := replaySessionEventLog(logPath)
	if err != nil {
		t.Fatalf("replay: %v", err)
	}
	if !replay.damaged {
		t.Fatal("replay.damaged = false, want true for broken chain")
	}
	for _, m := range replay.msgs {
		if m.Content == "lost" {
			t.Fatal("broken-chain record leaked into replayed transcript")
		}
	}
}

func TestReplayRejectsUnsupportedSchemaVersion(t *testing.T) {
	dir := t.TempDir()
	logPath := filepath.Join(dir, "future.events.jsonl")
	if err := os.WriteFile(logPath, []byte(`{"schema_version":99,"type":"replace","messages":[]}`+"\n"), 0o644); err != nil {
		t.Fatalf("write future log: %v", err)
	}
	if _, err := replaySessionEventLog(logPath); err == nil {
		t.Fatal("replay of future schema succeeded, want hard error (no silent truncation of newer writers)")
	}
}

func TestReplaySessionEventLogEnforcesResourceBudgetsWithoutMutation(t *testing.T) {
	dir := t.TempDir()
	logPath := filepath.Join(dir, "bounded.events.jsonl")
	replace := `{"schema_version":1,"type":"replace","messages":[{"role":"system","content":"sys"},{"role":"user","content":"prompt"}]}` + "\n"
	appendEvent := `{"schema_version":1,"type":"append","message_index":2,"messages":[{"role":"assistant","content":"reply"}]}` + "\n"
	contents := replace + appendEvent
	if err := os.WriteFile(logPath, []byte(contents), 0o600); err != nil {
		t.Fatalf("write event log: %v", err)
	}

	tests := []struct {
		name     string
		limits   sessionReplayLimits
		resource string
	}{
		{
			name: "encoded bytes",
			limits: sessionReplayLimits{
				maxBytes: int64(len(contents) - 1), maxRecords: 10, maxMessages: 10,
			},
			resource: "encoded_bytes",
		},
		{
			name: "event records",
			limits: sessionReplayLimits{
				maxBytes: int64(len(contents) + 1), maxRecords: 1, maxMessages: 10,
			},
			resource: "event_records",
		},
		{
			name: "messages",
			limits: sessionReplayLimits{
				maxBytes: int64(len(contents) + 1), maxRecords: 10, maxMessages: 1,
			},
			resource: "messages",
		},
		{
			name: "aggregate messages across records",
			limits: sessionReplayLimits{
				maxBytes: int64(len(contents) + 1), maxRecords: 10, maxMessages: 2,
			},
			resource: "messages",
		},
	}
	for _, tc := range tests {
		t.Run(tc.name, func(t *testing.T) {
			if _, err := replaySessionEventLogWithLimits(logPath, tc.limits, nil); !errors.Is(err, ErrSessionReplayLimitExceeded) {
				t.Fatalf("replay error = %v, want ErrSessionReplayLimitExceeded", err)
			} else {
				var limitErr *SessionReplayLimitError
				if !errors.As(err, &limitErr) || limitErr.Resource != tc.resource {
					t.Fatalf("limit error = %#v, want resource %q", limitErr, tc.resource)
				}
				if strings.Contains(err.Error(), logPath) {
					t.Fatalf("user-facing error leaked local path: %q", err)
				}
			}
			got, err := os.ReadFile(logPath)
			if err != nil {
				t.Fatalf("read event log after rejection: %v", err)
			}
			if string(got) != contents {
				t.Fatal("resource-budget rejection modified the event log")
			}
		})
	}
}

func TestReplayChecksMessageBudgetBeforeDecodingOverLimitElement(t *testing.T) {
	logPath := filepath.Join(t.TempDir(), "bounded-before-decode.events.jsonl")
	// The third element is valid JSON but cannot decode into provider.Message.
	// A two-message budget must reject it before attempting that decode.
	events := `{"schema_version":1,"type":"replace","messages":[{}, {}, 42]}` + "\n"
	if err := os.WriteFile(logPath, []byte(events), 0o600); err != nil {
		t.Fatalf("write event log: %v", err)
	}

	replay, err := replaySessionEventLogWithLimits(logPath, sessionReplayLimits{
		maxBytes: int64(len(events) + 1), maxRecords: 10, maxMessages: 2,
	}, nil)
	if !errors.Is(err, ErrSessionReplayLimitExceeded) {
		t.Fatalf("replay error = %v, want message replay limit", err)
	}
	var limitErr *SessionReplayLimitError
	if !errors.As(err, &limitErr) || limitErr.Resource != "messages" || limitErr.Value != 3 {
		t.Fatalf("limit error = %#v, want third message rejected before decode", limitErr)
	}
	if replay.records != 0 || len(replay.msgs) != 0 {
		t.Fatalf("partial over-limit record was applied: records=%d messages=%d", replay.records, len(replay.msgs))
	}
}

func TestReplayChecksCollectionBudgetBeforeDecodingOverLimitElement(t *testing.T) {
	logPath := filepath.Join(t.TempDir(), "bounded-collection-before-decode.events.jsonl")
	// The third tool call cannot decode into provider.ToolCall. A two-item
	// collection budget must reject it before constructing the typed slice.
	events := `{"schema_version":1,"type":"replace","messages":[{"role":"assistant","tool_calls":[{}, {}, 42]}]}` + "\n"
	if err := os.WriteFile(logPath, []byte(events), 0o600); err != nil {
		t.Fatalf("write event log: %v", err)
	}

	replay, err := replaySessionEventLogWithLimits(logPath, sessionReplayLimits{
		maxBytes: int64(len(events) + 1), maxRecords: 10, maxMessages: 10, maxCollectionItems: 2,
	}, nil)
	if !errors.Is(err, ErrSessionReplayLimitExceeded) {
		t.Fatalf("replay error = %v, want collection replay limit", err)
	}
	var limitErr *SessionReplayLimitError
	if !errors.As(err, &limitErr) || limitErr.Resource != "message_collection_items" || limitErr.Value != 3 {
		t.Fatalf("limit error = %#v, want third collection item rejected before decode", limitErr)
	}
	if replay.records != 0 || len(replay.msgs) != 0 {
		t.Fatalf("partial over-limit record was applied: records=%d messages=%d", replay.records, len(replay.msgs))
	}
	if got, readErr := os.ReadFile(logPath); readErr != nil || string(got) != events {
		t.Fatalf("event log changed after refusal: bytes=%q err=%v", got, readErr)
	}
}

func TestReplayCollectionBudgetAggregatesAcrossRecords(t *testing.T) {
	logPath := filepath.Join(t.TempDir(), "aggregate-collection-budget.events.jsonl")
	replace := `{"schema_version":1,"type":"replace","messages":[{"role":"user","images":["one"]}]}` + "\n"
	appendEvent := `{"schema_version":1,"type":"append","message_index":1,"messages":[{"role":"assistant","tool_calls":[{},{}]}]}` + "\n"
	events := replace + appendEvent
	if err := os.WriteFile(logPath, []byte(events), 0o600); err != nil {
		t.Fatalf("write event log: %v", err)
	}

	replay, err := replaySessionEventLogWithLimits(logPath, sessionReplayLimits{
		maxBytes: int64(len(events) + 1), maxRecords: 10, maxMessages: 10, maxCollectionItems: 2,
	}, nil)
	if !errors.Is(err, ErrSessionReplayLimitExceeded) {
		t.Fatalf("replay error = %v, want aggregate collection replay limit", err)
	}
	var limitErr *SessionReplayLimitError
	if !errors.As(err, &limitErr) || limitErr.Resource != "message_collection_items" || limitErr.Value != 3 {
		t.Fatalf("limit error = %#v, want third live collection item rejected", limitErr)
	}
	if replay.records != 1 || len(replay.msgs) != 1 || replay.collectionItems != 1 {
		t.Fatalf("replay prefix = records:%d messages:%d collections:%d, want first record only",
			replay.records, len(replay.msgs), replay.collectionItems)
	}
}

func TestLoadSessionMessagesDoesNotFallbackAfterEventReplayBudget(t *testing.T) {
	path := filepath.Join(t.TempDir(), "session.jsonl")
	checkpoint := `{"role":"system","content":"older checkpoint"}` + "\n"
	if err := os.WriteFile(path, []byte(checkpoint), 0o600); err != nil {
		t.Fatalf("write checkpoint: %v", err)
	}
	logPath := store.SessionEventLog(path)
	events := `{"schema_version":1,"type":"replace","messages":[{"role":"system","content":"newer event state"},{"role":"user","content":"must not disappear"}]}` + "\n"
	if err := os.WriteFile(logPath, []byte(events), 0o600); err != nil {
		t.Fatalf("write event log: %v", err)
	}

	msgs, fromEvents, damaged, err := loadSessionMessagesWithLimits(path, sessionReplayLimits{
		maxBytes: int64(len(events) + 1), maxRecords: 10, maxMessages: 1,
	}, nil)
	if !errors.Is(err, ErrSessionReplayLimitExceeded) {
		t.Fatalf("load error = %v, want ErrSessionReplayLimitExceeded", err)
	}
	if msgs != nil || !fromEvents || damaged {
		t.Fatalf("load result = msgs:%v fromEvents:%v damaged:%v, want hard event-log refusal", msgs, fromEvents, damaged)
	}
	if got, readErr := os.ReadFile(path); readErr != nil || string(got) != checkpoint {
		t.Fatalf("checkpoint changed after refusal: bytes=%q err=%v", got, readErr)
	}
	if got, readErr := os.ReadFile(logPath); readErr != nil || string(got) != events {
		t.Fatalf("event log changed after refusal: bytes=%q err=%v", got, readErr)
	}
}

func TestProbeSessionEventLogReadsOnlyNativeHeader(t *testing.T) {
	path := filepath.Join(t.TempDir(), "session.jsonl")
	logPath := store.SessionEventLog(path)
	largeRecord := `{"schema_version":1,"type":"replace","messages":[{"role":"user","content":"` +
		strings.Repeat("x", int(sessionEventProbeMaxBytes*2)) + `"}]}` + "\n"
	if err := os.WriteFile(logPath, []byte(largeRecord), 0o600); err != nil {
		t.Fatalf("write event log: %v", err)
	}
	probe, err := probeSessionEventLogWithLimits(path, sessionReplayLimits{
		maxBytes: 128, maxRecords: 10, maxMessages: 10,
	})
	if err != nil {
		t.Fatalf("probe: %v", err)
	}
	if !probe.native || probe.size != int64(len(largeRecord)) {
		t.Fatalf("probe = %+v, want native size %d", probe, len(largeRecord))
	}
}

func TestLoadSessionMessagesAcceptsReorderedEventHeader(t *testing.T) {
	path := filepath.Join(t.TempDir(), "session.jsonl")
	checkpoint := `{"role":"system","content":"older checkpoint"}` + "\n"
	if err := os.WriteFile(path, []byte(checkpoint), 0o600); err != nil {
		t.Fatalf("write checkpoint: %v", err)
	}
	content := "newer event state " + strings.Repeat("x", int(sessionEventProbeMaxBytes*2))
	// schema_version deliberately follows a messages payload larger than the
	// prefix probe. Valid in-budget JSON must remain field-order independent.
	events := `{"type":"replace","messages":[{"role":"system","content":"sys"},{"role":"user","content":"` +
		content + `"}],"schema_version":1}` + "\n"
	if err := os.WriteFile(store.SessionEventLog(path), []byte(events), 0o600); err != nil {
		t.Fatalf("write reordered event log: %v", err)
	}

	msgs, fromEvents, damaged, err := loadSessionMessages(path)
	if err != nil {
		t.Fatalf("load reordered event log: %v", err)
	}
	if !fromEvents || damaged {
		t.Fatalf("load result fromEvents=%v damaged=%v, want clean native replay", fromEvents, damaged)
	}
	if len(msgs) != 2 || msgs[1].Content != content {
		t.Fatalf("loaded messages = %d, want reordered event state", len(msgs))
	}
}

func TestDefaultSaveBootstrapsEventLog(t *testing.T) {
	path := filepath.Join(t.TempDir(), "session.jsonl")
	s := NewSession("sys")
	s.Add(provider.Message{Role: provider.RoleUser, Content: "one-shot"})
	if err := s.Save(path); err != nil {
		t.Fatalf("Save: %v", err)
	}
	if _, err := os.Stat(store.SessionEventLog(path)); err != nil {
		t.Fatalf("default save did not create an event log: %v", err)
	}
	if _, err := os.Stat(store.SessionEventIndex(path)); err != nil {
		t.Fatalf("default save did not create an event index: %v", err)
	}
}

func TestDefaultSaveRejectsDivergedOverwrite(t *testing.T) {
	path := filepath.Join(t.TempDir(), "session.jsonl")
	winner := sessionWithTurns(t, path, 3).Snapshot()

	stale := NewSession("sys")
	stale.Add(provider.Message{Role: provider.RoleUser, Content: "stale state"})
	if err := stale.Save(path); !errors.Is(err, ErrSessionSnapshotConflict) {
		t.Fatalf("diverged Save error = %v, want ErrSessionSnapshotConflict", err)
	}
	loaded, err := LoadSession(path)
	if err != nil {
		t.Fatalf("LoadSession: %v", err)
	}
	if !messagesEqualForStorageList(loaded.Messages, winner) {
		t.Fatalf("default Save replaced newer transcript: got %d messages, want %d", len(loaded.Messages), len(winner))
	}
}

func TestEventLogCompactionBoundsGrowth(t *testing.T) {
	path := filepath.Join(t.TempDir(), "session.jsonl")
	s := NewSession("sys")
	filler := strings.Repeat("y", 8<<10)
	// Repeated rewrites (each a full replace event) must not grow the log
	// without bound: once past the threshold the log folds to one event.
	for i := range 60 {
		s.Replace([]provider.Message{
			{Role: provider.RoleSystem, Content: "sys"},
			{Role: provider.RoleUser, Content: filler},
			{Role: provider.RoleAssistant, Content: strings.Repeat("z", i+1)},
		})
		if err := s.SaveRewrite(path); err != nil {
			t.Fatalf("SaveRewrite %d: %v", i, err)
		}
	}
	_, contentBytes, err := digestAndSizeSessionMessages(s.Snapshot())
	if err != nil {
		t.Fatalf("digest: %v", err)
	}
	logSize := sessionEventLogSize(path)
	limit := sessionEventLogCompactFloor
	if scaled := contentBytes * sessionEventLogCompactFactor; scaled > limit {
		limit = scaled
	}
	// One post-compaction replace event of slack is allowed.
	if logSize > limit+contentBytes+4096 {
		t.Fatalf("event log grew unbounded: size=%d limit=%d content=%d", logSize, limit, contentBytes)
	}
	loaded, err := LoadSession(path)
	if err != nil {
		t.Fatalf("LoadSession after compaction churn: %v", err)
	}
	if got := loaded.Messages[len(loaded.Messages)-1].Content; got != strings.Repeat("z", 60) {
		t.Fatalf("compacted transcript tail wrong: %q", got[:min(8, len(got))])
	}
	anchor, err := loadSessionMessagesFromJSONL(path, nil)
	if err != nil {
		t.Fatalf("read anchor: %v", err)
	}
	if got := anchor[len(anchor)-1].Content; got != strings.Repeat("z", 60) {
		t.Fatal("anchor not refreshed by checkpoint compaction")
	}
}

func TestConcurrentLoadDuringAppendsStaysConsistent(t *testing.T) {
	path := filepath.Join(t.TempDir(), "session.jsonl")
	s := NewSession("sys")
	s.Add(provider.Message{Role: provider.RoleUser, Content: "seed"})
	if err := s.SaveSnapshot(path); err != nil {
		t.Fatalf("seed SaveSnapshot: %v", err)
	}

	stop := make(chan struct{})
	var wg sync.WaitGroup
	wg.Add(1)
	errCh := make(chan error, 1)
	go func() {
		defer wg.Done()
		for {
			select {
			case <-stop:
				return
			default:
			}
			loaded, err := LoadSession(path)
			if err != nil {
				select {
				case errCh <- err:
				default:
				}
				return
			}
			if loaded.eventLogDamaged {
				select {
				case errCh <- os.ErrInvalid:
				default:
				}
				return
			}
		}
	}()
	for i := range 40 {
		s.Add(provider.Message{Role: provider.RoleAssistant, Content: strings.Repeat("a", 512)})
		if err := s.SaveSnapshot(path); err != nil {
			t.Fatalf("SaveSnapshot %d: %v", i, err)
		}
	}
	close(stop)
	wg.Wait()
	select {
	case err := <-errCh:
		t.Fatalf("concurrent LoadSession failed or saw damage: %v", err)
	default:
	}
}

func TestSessionsShareContentSeesEventLogDivergence(t *testing.T) {
	dir := t.TempDir()
	pathA := filepath.Join(dir, "a.jsonl")
	pathB := filepath.Join(dir, "b.jsonl")
	a := sessionWithTurns(t, pathA, 1)
	_ = sessionWithTurns(t, pathB, 1)

	same, err := SessionsShareContent(pathA, pathB)
	if err != nil {
		t.Fatalf("SessionsShareContent: %v", err)
	}
	if !same {
		t.Fatal("identical transcripts reported as different")
	}

	// Grow A normally, then restore its old compatibility checkpoint to model a
	// crash or an older Reasonix build that did not advance the display read
	// model. Transcript equality must still follow the event log.
	anchorB, err := os.ReadFile(pathB)
	if err != nil {
		t.Fatalf("read checkpoint B: %v", err)
	}
	a.Add(provider.Message{Role: provider.RoleUser, Content: "diverged"})
	if err := a.SaveSnapshot(pathA); err != nil {
		t.Fatalf("SaveSnapshot diverge: %v", err)
	}
	if err := os.WriteFile(pathA, anchorB, 0o600); err != nil {
		t.Fatalf("restore stale checkpoint A: %v", err)
	}
	anchorA, _ := os.ReadFile(pathA)
	if string(anchorA) != string(anchorB) {
		t.Fatal("test setup did not preserve byte-identical checkpoints")
	}
	same, err = SessionsShareContent(pathA, pathB)
	if err != nil {
		t.Fatalf("SessionsShareContent after divergence: %v", err)
	}
	if same {
		t.Fatal("diverged transcripts reported as identical")
	}
}

func TestLoadSessionUserMessagesSeesEventLogTurns(t *testing.T) {
	path := filepath.Join(t.TempDir(), "session.jsonl")
	s := NewSession("sys")
	s.Add(provider.Message{Role: provider.RoleUser, Content: "first prompt"})
	if err := s.SaveSnapshot(path); err != nil {
		t.Fatalf("SaveSnapshot: %v", err)
	}
	s.Add(provider.Message{Role: provider.RoleAssistant, Content: "reply"})
	s.Add(provider.Message{Role: provider.RoleUser, Content: "second prompt"})
	if err := s.SaveSnapshot(path); err != nil {
		t.Fatalf("SaveSnapshot append: %v", err)
	}

	users, err := LoadSessionUserMessages(path)
	if err != nil {
		t.Fatalf("LoadSessionUserMessages: %v", err)
	}
	if len(users) != 2 || users[0].Message.Content != "first prompt" || users[1].Message.Content != "second prompt" {
		t.Fatalf("user messages = %+v, want both prompts", users)
	}
	if users[1].At.IsZero() {
		t.Fatal("appended prompt lost its event timestamp")
	}
}

func TestLoadSessionUserMessagesDoesNotFallbackAfterEventReplayBudget(t *testing.T) {
	path := filepath.Join(t.TempDir(), "session.jsonl")
	checkpoint := `{"role":"user","content":"older checkpoint prompt"}` + "\n"
	if err := os.WriteFile(path, []byte(checkpoint), 0o600); err != nil {
		t.Fatalf("write checkpoint: %v", err)
	}
	logPath := store.SessionEventLog(path)
	events := `{"schema_version":1,"type":"replace","messages":[{"role":"user","content":"newer prompt"},{"role":"assistant","content":"reply"}]}` + "\n"
	if err := os.WriteFile(logPath, []byte(events), 0o600); err != nil {
		t.Fatalf("write event log: %v", err)
	}

	users, err := loadSessionUserMessagesWithLimits(path, sessionReplayLimits{
		maxBytes: int64(len(events) + 1), maxRecords: 10, maxMessages: 1, maxCollectionItems: 10,
	})
	if !errors.Is(err, ErrSessionReplayLimitExceeded) {
		t.Fatalf("load error = %v, want ErrSessionReplayLimitExceeded", err)
	}
	if users != nil {
		t.Fatalf("user messages = %+v, want no stale checkpoint fallback", users)
	}
	if got, readErr := os.ReadFile(path); readErr != nil || string(got) != checkpoint {
		t.Fatalf("checkpoint changed after refusal: bytes=%q err=%v", got, readErr)
	}
	if got, readErr := os.ReadFile(logPath); readErr != nil || string(got) != events {
		t.Fatalf("event log changed after refusal: bytes=%q err=%v", got, readErr)
	}
}

func TestLoadSessionUserMessagesDoesNotFallbackFromFutureEventSchema(t *testing.T) {
	path := filepath.Join(t.TempDir(), "session.jsonl")
	checkpoint := `{"role":"user","content":"older checkpoint prompt"}` + "\n"
	if err := os.WriteFile(path, []byte(checkpoint), 0o600); err != nil {
		t.Fatalf("write checkpoint: %v", err)
	}
	events := `{"schema_version":99,"type":"replace","messages":[{"role":"user","content":"future prompt"}]}` + "\n"
	if err := os.WriteFile(store.SessionEventLog(path), []byte(events), 0o600); err != nil {
		t.Fatalf("write event log: %v", err)
	}

	users, err := LoadSessionUserMessages(path)
	if err == nil || !strings.Contains(err.Error(), "uses schema 99") {
		t.Fatalf("load error = %v, want future-schema refusal", err)
	}
	if users != nil {
		t.Fatalf("user messages = %+v, want no stale checkpoint fallback", users)
	}
}

func TestSessionEventLogPreservesUserCreatedAt(t *testing.T) {
	path := filepath.Join(t.TempDir(), "session.jsonl")
	want := time.Date(2026, 7, 16, 8, 30, 0, 0, time.UTC).UnixMilli()
	s := NewSession("sys")
	s.Add(provider.Message{Role: provider.RoleUser, Content: "timed prompt", CreatedAt: want})
	if err := s.SaveSnapshot(path); err != nil {
		t.Fatalf("SaveSnapshot: %v", err)
	}

	loaded, err := LoadSession(path)
	if err != nil {
		t.Fatalf("LoadSession: %v", err)
	}
	msgs := loaded.Snapshot()
	if len(msgs) != 2 || msgs[1].CreatedAt != want {
		t.Fatalf("loaded messages = %+v, want user createdAt %d", msgs, want)
	}
}

func TestSessionDigestIgnoresUserCreatedAt(t *testing.T) {
	withoutTime := []provider.Message{
		{Role: provider.RoleSystem, Content: "sys"},
		{Role: provider.RoleUser, Content: "prompt"},
	}
	withTime := append([]provider.Message(nil), withoutTime...)
	withTime[1].CreatedAt = 1_718_000_000_000

	withoutDigest, withoutSize, err := digestAndSizeSessionMessages(withoutTime)
	if err != nil {
		t.Fatalf("digest without createdAt: %v", err)
	}
	withDigest, withSize, err := digestAndSizeSessionMessages(withTime)
	if err != nil {
		t.Fatalf("digest with createdAt: %v", err)
	}
	if withoutDigest != withDigest || withoutSize != withSize {
		t.Fatalf("local createdAt changed transcript identity: digestEqual=%v size=%d/%d", withoutDigest == withDigest, withoutSize, withSize)
	}
	if !messagesHavePrefix(withTime, withoutTime) || !messagesHavePrefix(withoutTime, withTime) {
		t.Fatal("local createdAt broke cross-version transcript prefix matching")
	}
	if depth := messagesPrefixDigestDepth(withTime, withoutDigest); depth != len(withTime) {
		t.Fatalf("createdAt-aware prefix digest depth = %d, want %d", depth, len(withTime))
	}
}

func TestSessionContentModTimeTracksEventLog(t *testing.T) {
	path := filepath.Join(t.TempDir(), "session.jsonl")
	s := sessionWithTurns(t, path, 1)
	s.Add(provider.Message{Role: provider.RoleUser, Content: "new"})
	if err := s.SaveSnapshot(path); err != nil {
		t.Fatalf("SaveSnapshot: %v", err)
	}
	// Filesystems such as macOS can expose coarse mtime resolution, so the
	// checkpoint and event log written by one save are allowed to have the
	// same timestamp. Make the ordering under test explicit after the save:
	// the checkpoint is a stale anchor while the event log remains current.
	old := time.Date(2020, 1, 1, 0, 0, 0, 0, time.UTC)
	if err := os.Chtimes(path, old, old); err != nil {
		t.Fatalf("age anchor: %v", err)
	}
	anchorInfo, err := os.Stat(path)
	if err != nil {
		t.Fatalf("stat anchor: %v", err)
	}
	if got := SessionContentModTime(path); !got.After(anchorInfo.ModTime()) {
		t.Fatalf("SessionContentModTime = %v, want newer than stale anchor %v", got, anchorInfo.ModTime())
	}
}