diff --git a/internal/frontend/lsp/debug_cross_document_test.go b/internal/frontend/lsp/debug_cross_document_test.go
new file mode 100644
index 0000000000..adc95b63bc
--- /dev/null
+++ b/internal/frontend/lsp/debug_cross_document_test.go
@@ -0,0 +1,90 @@
+package lsp
+
+import (
+	"context"
+	"errors"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"go.lsp.dev/jsonrpc2"
+	"go.lsp.dev/protocol"
+	"go.lsp.dev/uri"
+)
+
+// A view debugs the behavior it exposes from another document, performed by an
+// object from a third; edits there move or end the session, duplicates are refused.
+func TestDebugTargetDeclaredInAnotherDocument(t *testing.T) {
+	ctx := context.Background()
+	split := strings.Index(debugMachine, "package MachineViews")
+	machines, views := debugMachine[:split], debugMachine[split:]
+	dir := t.TempDir()
+	open := func(t *testing.T, s *Server, name, src string) uri.URI {
+		t.Helper()
+		docURI := uri.File(filepath.Join(dir, name))
+		if err := s.DidOpen(ctx, &protocol.DidOpenTextDocumentParams{
+			TextDocument: protocol.TextDocumentItem{URI: docURI, LanguageID: "sysml", Version: 1, Text: src},
+		}); err != nil {
+			t.Fatalf("DidOpen %s: %v", name, err)
+		}
+		return docURI
+	}
+	s, viewsURI, rec := debugServer(t, "views.sysml", views)
+	machinesURI := open(t, s, "machines.sysml", machines)
+	open(t, s, "robots.sysml", "package Robots { part def Rover { exhibit state ops : Machines::Ops; } }\n")
+	r := render(t, s, viewsURI, "MachineViews::opsView")
+	id := ids(t, r)
+
+	snap := mustDebug(t, s, MethodDebugStart, &debugStartParams{
+		TextDocument: protocol.TextDocumentIdentifier{URI: viewsURI},
+		View:         "MachineViews::opsView", Target: "Machines::Ops", Object: "Robots::Rover",
+	})
+	if snap.Target != "Machines::Ops" || snap.Object != "Robots::Rover" || snap.Root != r.Nodes[0].ID {
+		t.Fatalf("start snapshot = %s", describe(snap))
+	}
+	wantState(t, snap, debugWaiting)
+	wantStrings(t, "initial active states", snap.ActiveStates, []string{id["motion"], id["idle"], id["clock"], id["waiting"]})
+
+	// An edit to the machine's document that leaves the machine as declared
+	// keeps the session running; one rewriting the machine ends it.
+	s.applyDidChange(ctx, uriToName(machinesURI), []rawContentChange{{Text: strings.Replace(machines, "attribute def Halt;", "attribute def Halt;\n\tattribute def Stop;", 1)}}, 2)
+	for _, moved := range rec.debugChanged() {
+		if moved.Session != snap.Session || moved.State == debugEnded {
+			t.Fatalf("debugChanged after an unrelated edit to the machine's document = %s", describe(moved))
+		}
+		wantStrings(t, "active states after an unrelated edit", moved.ActiveStates, snap.ActiveStates)
+	}
+	s.applyDidChange(ctx, uriToName(machinesURI), []rawContentChange{{Text: strings.Replace(machines, "state elapsed;", "state elapsed;\n\t\tstate cooling;", 1)}}, 3)
+	changed := rec.debugChanged()
+	last := changed[len(changed)-1]
+	if last.Session != snap.Session || last.State != debugEnded || !strings.Contains(last.Reason, "Machines::Ops was edited") {
+		t.Fatalf("debugChanged after the machine was edited = %s", describe(last))
+	}
+
+	// Closing the machine's document ends a session on it too.
+	snap = mustDebug(t, s, MethodDebugStart, &debugStartParams{
+		TextDocument: protocol.TextDocumentIdentifier{URI: viewsURI}, View: "MachineViews::opsView", Target: "Machines::Ops",
+	})
+	if err := s.DidClose(ctx, &protocol.DidCloseTextDocumentParams{TextDocument: protocol.TextDocumentIdentifier{URI: machinesURI}}); err != nil {
+		t.Fatalf("DidClose: %v", err)
+	}
+	changed = rec.debugChanged()
+	last = changed[len(changed)-1]
+	if last.Session != snap.Session || last.State != debugEnded || !strings.Contains(last.Reason, "machines.sysml was closed") {
+		t.Fatalf("debugChanged after closing the machine's document = %s", describe(last))
+	}
+
+	// The same name declared by two documents names neither.
+	open(t, s, "machines.sysml", machines)
+	spareURI := open(t, s, "spare.sysml", machines)
+	_, err := s.DebugStart(&debugStartParams{
+		TextDocument: protocol.TextDocumentIdentifier{URI: viewsURI}, View: "MachineViews::opsView", Target: "Machines::Ops",
+	})
+	if !errors.Is(err, ErrDebugTarget) || !strings.Contains(err.Error(), machinesURI.Filename()+", "+spareURI.Filename()) {
+		t.Fatalf("start of an ambiguous target: err = %v, want %v naming both documents", err, ErrDebugTarget)
+	}
+	var wire *jsonrpc2.Error
+	if !errors.As(err, &wire) || wire.Code != jsonrpc2.InvalidParams {
+		t.Errorf("err = %v, want an InvalidParams reply", err)
+	}
+}
diff --git a/internal/frontend/lsp/debug_test.go b/internal/frontend/lsp/debug_test.go
index 92c1165a49..8a0649000e 100644
--- a/internal/frontend/lsp/debug_test.go
+++ b/internal/frontend/lsp/debug_test.go
@@ -133,7 +133,7 @@ func debugServer(t *testing.T, name, src string) (*Server, uri.URI, *debugRecord
 	rec := &debugRecorder{}
 	s.client = rec
 	s.notifier = rec
-	docURI := uri.File(name)
+	docURI := testDocURI(t, name)
 	if err := s.DidOpen(context.Background(), &protocol.DidOpenTextDocumentParams{
 		TextDocument: protocol.TextDocumentItem{URI: docURI, LanguageID: "sysml", Version: 1, Text: src},
 	}); err != nil {
@@ -358,7 +358,7 @@ func TestDebugProtocolShapes(t *testing.T) {
 // object, a session not live, a node not drawn or a signal not taken is refused
 // with a typed InvalidParams error.
 func TestDebugRefusesWhatItCannotRun(t *testing.T) {
-	s, docURI, _ := debugServer(t, "/w/m.sysml", debugMachine+`
+	s, docURI, _ := debugServer(t, "m.sysml", debugMachine+`
 package Other {
 	part def Widget;
 	view widgets : TreeView { expose Other::Widget; }
@@ -435,7 +435,7 @@ package Other {
 // A state machine session reports active states per region, fired transitions
 // and queued events in render IDs; signals, the clock and breakpoints drive it.
 func TestDebugStateMachineSession(t *testing.T) {
-	s, docURI, _ := debugServer(t, "/w/m.sysml", debugMachine)
+	s, docURI, _ := debugServer(t, "m.sysml", debugMachine)
 	r := render(t, s, docURI, "MachineViews::opsView")
 	id := ids(t, r)
 	edge := func(from, to string) string { return id[from] + "->" + id[to] }
@@ -577,7 +577,7 @@ package MachineViews {
 // An entry transition into a nested state is taken from the start marker of the
 // body it is written in — the machine's — not that of the state it lands in.
 func TestDebugEntryTransitionIntoANestedState(t *testing.T) {
-	s, docURI, _ := debugServer(t, "/w/m.sysml", debugDeep)
+	s, docURI, _ := debugServer(t, "m.sysml", debugDeep)
 	r := render(t, s, docURI, "MachineViews::deepView")
 	id := ids(t, r)
 	var machineStart string
@@ -601,7 +601,7 @@ func TestDebugEntryTransitionIntoANestedState(t *testing.T) {
 // A continue runs what is due now and holds the clock: an event due later
 // leaves the machine waiting, at the same instant, until an advance reaches it.
 func TestDebugContinueHoldsTheClock(t *testing.T) {
-	s, docURI, _ := debugServer(t, "/w/m.sysml", debugMachine)
+	s, docURI, _ := debugServer(t, "m.sysml", debugMachine)
 	id := ids(t, render(t, s, docURI, "MachineViews::opsView"))
 	snap := mustDebug(t, s, MethodDebugStart, &debugStartParams{
 		TextDocument: protocol.TextDocumentIdentifier{URI: docURI},
@@ -670,7 +670,7 @@ package TransientViews {
 // An advance pauses at a breakpoint state as it becomes active, a state left
 // again at the same instant included, the clock held at that instant.
 func TestDebugAdvancePausesOnATransientState(t *testing.T) {
-	s, docURI, _ := debugServer(t, "/w/t.sysml", debugTransient)
+	s, docURI, _ := debugServer(t, "t.sysml", debugTransient)
 	id := ids(t, render(t, s, docURI, "TransientViews::descentView"))
 	snap := mustDebug(t, s, MethodDebugStart, &debugStartParams{
 		TextDocument: protocol.TextDocumentIdentifier{URI: docURI},
@@ -759,7 +759,7 @@ package BViews {
 // does: the machine's own Go rather than the first Go declared in the document,
 // and a signal declared in its body; a qualified name still names what it says.
 func TestDebugSendResolvesSignalInTargetScope(t *testing.T) {
-	s, docURI, _ := debugServer(t, "/w/s.sysml", debugSameNamedSignals)
+	s, docURI, _ := debugServer(t, "s.sysml", debugSameNamedSignals)
 	id := ids(t, render(t, s, docURI, "BViews::machineView"))
 	snap := mustDebug(t, s, MethodDebugStart, &debugStartParams{
 		TextDocument: protocol.TextDocumentIdentifier{URI: docURI},
@@ -792,7 +792,7 @@ func TestDebugSendResolvesSignalInTargetScope(t *testing.T) {
 // A breakpoint on a pseudostate pauses the run once the dispatch routed through
 // it completes, the pseudostate reported as where it paused.
 func TestDebugBreakpointOnAPseudostatePauses(t *testing.T) {
-	s, docURI, _ := debugServer(t, "/w/j.sysml", debugJunction)
+	s, docURI, _ := debugServer(t, "j.sysml", debugJunction)
 	id := ids(t, render(t, s, docURI, "RoutingViews::opsView"))
 	snap := mustDebug(t, s, MethodDebugStart, &debugStartParams{
 		TextDocument: protocol.TextDocumentIdentifier{URI: docURI},
@@ -820,7 +820,7 @@ func TestDebugBreakpointOnAPseudostatePauses(t *testing.T) {
 // A breakpoint on the machine's `done` pauses the run standing on it, before the
 // machine completes; the next step completes it.
 func TestDebugBreakpointOnDonePausesBeforeCompletion(t *testing.T) {
-	s, docURI, _ := debugServer(t, "/w/h.sysml", `package Halting {
+	s, docURI, _ := debugServer(t, "h.sysml", `package Halting {
 	attribute def Halt;
 	state def Runner {
 		entry; then idle;
@@ -872,7 +872,7 @@ package HaltingViews {
 // A step that lands a token on an action breakpoint pauses there, as a continue
 // does; the step after moves it past the breakpoint.
 func TestDebugStepPausesAtAnActionBreakpoint(t *testing.T) {
-	s, docURI, _ := debugServer(t, "/w/f.sysml", debugFlow)
+	s, docURI, _ := debugServer(t, "f.sysml", debugFlow)
 	id := ids(t, render(t, s, docURI, "FlowViews::driveView"))
 	snap := mustDebug(t, s, MethodDebugStart, &debugStartParams{
 		TextDocument: protocol.TextDocumentIdentifier{URI: docURI}, View: "FlowViews::driveView", Target: "Flows::Drive",
@@ -904,7 +904,7 @@ func TestDebugStepPausesAtAnActionBreakpoint(t *testing.T) {
 // on its fork, returning the session and the rendering's IDs.
 func pausedAtSplit(t *testing.T) (*Server, string, map[string]string) {
 	t.Helper()
-	s, docURI, _ := debugServer(t, "/w/f.sysml", debugFlow)
+	s, docURI, _ := debugServer(t, "f.sysml", debugFlow)
 	id := ids(t, render(t, s, docURI, "FlowViews::driveView"))
 	snap := mustDebug(t, s, MethodDebugStart, &debugStartParams{
 		TextDocument: protocol.TextDocumentIdentifier{URI: docURI}, View: "FlowViews::driveView", Target: "Flows::Drive",
@@ -1004,7 +1004,7 @@ package ReusedViews {
 // A breakpoint on one drawing of a node a nested flow reuses stops the run at
 // that occurrence only, not at the same declaration another nested flow runs.
 func TestDebugBreakpointOnAReusedNodeStopsAtItsOccurrence(t *testing.T) {
-	s, docURI, _ := debugServer(t, "/w/r.sysml", debugReused)
+	s, docURI, _ := debugServer(t, "r.sysml", debugReused)
 	r := render(t, s, docURI, "ReusedViews::twiceView")
 	var a, b, lookInA, lookInB string
 	for _, n := range r.Nodes {
@@ -1052,7 +1052,7 @@ func TestDebugBreakpointOnAReusedNodeStopsAtItsOccurrence(t *testing.T) {
 // found on a breakpoint: a token still held at one already stopped at does not
 // stand in for the one the run has just reached.
 func TestDebugPausedAtIsTheBreakpointReachedNotTheFirstTokenOnOne(t *testing.T) {
-	s, docURI, _ := debugServer(t, "/w/f.sysml", debugFlow)
+	s, docURI, _ := debugServer(t, "f.sysml", debugFlow)
 	id := ids(t, render(t, s, docURI, "FlowViews::driveView"))
 	snap := mustDebug(t, s, MethodDebugStart, &debugStartParams{
 		TextDocument: protocol.TextDocumentIdentifier{URI: docURI}, View: "FlowViews::driveView", Target: "Flows::Drive",
@@ -1115,7 +1115,7 @@ package CountingViews {
 // already runs, so its timed effect happens once; an object exhibiting it twice
 // is ambiguous.
 func TestDebugStartAttachesToThePerformersMachine(t *testing.T) {
-	s, docURI, _ := debugServer(t, "/w/c.sysml", debugCounter)
+	s, docURI, _ := debugServer(t, "c.sysml", debugCounter)
 	id := ids(t, render(t, s, docURI, "CountingViews::opsView"))
 	snap := mustDebug(t, s, MethodDebugStart, &debugStartParams{
 		TextDocument: protocol.TextDocumentIdentifier{URI: docURI},
@@ -1143,7 +1143,7 @@ func TestDebugStartAttachesToThePerformersMachine(t *testing.T) {
 // the last snapshot read from: each snapshot releases what the one before it
 // reported, so a long-lived session's record stays bounded while the counts go on.
 func TestDebugSessionReleasesTheHistoryItReports(t *testing.T) {
-	s, docURI, _ := debugServer(t, "/w/m.sysml", debugMachine)
+	s, docURI, _ := debugServer(t, "m.sysml", debugMachine)
 	snap := mustDebug(t, s, MethodDebugStart, &debugStartParams{
 		TextDocument: protocol.TextDocumentIdentifier{URI: docURI},
 		View:         "MachineViews::opsView", Target: "Machines::Ops", Object: "Machines::Robot",
@@ -1165,7 +1165,7 @@ func TestDebugSessionReleasesTheHistoryItReports(t *testing.T) {
 		t.Errorf("after a request firing nothing taken %d, kept %d of %d; want none, none kept, %d counted", len(snap.Taken), len(machine.FiredTransitions()), machine.FiredCount(), fired+1)
 	}
 
-	s, docURI, _ = debugServer(t, "/w/f.sysml", debugFlow)
+	s, docURI, _ = debugServer(t, "f.sysml", debugFlow)
 	snap = mustDebug(t, s, MethodDebugStart, &debugStartParams{
 		TextDocument: protocol.TextDocumentIdentifier{URI: docURI}, View: "FlowViews::driveView", Target: "Flows::Drive",
 	})
@@ -1186,7 +1186,7 @@ func TestDebugSessionReleasesTheHistoryItReports(t *testing.T) {
 // A machine's queue shows every message pending in its context, a message no
 // state of the machine accepts now included: it is in flight all the same.
 func TestDebugMachineQueueShowsEveryPendingMessage(t *testing.T) {
-	s, docURI, _ := debugServer(t, "/w/m.sysml", debugMachine)
+	s, docURI, _ := debugServer(t, "m.sysml", debugMachine)
 	snap := mustDebug(t, s, MethodDebugStart, &debugStartParams{
 		TextDocument: protocol.TextDocumentIdentifier{URI: docURI},
 		View:         "MachineViews::opsView", Target: "Machines::Ops", Object: "Machines::Robot",
@@ -1211,7 +1211,7 @@ func TestDebugMachineQueueShowsEveryPendingMessage(t *testing.T) {
 // An action session reports every token (forked, nested, parked on the clock or
 // a signal, held at a join) with the edges it took, in the rendering's IDs.
 func TestDebugActionSession(t *testing.T) {
-	s, docURI, _ := debugServer(t, "/w/f.sysml", debugFlow)
+	s, docURI, _ := debugServer(t, "f.sysml", debugFlow)
 	r := render(t, s, docURI, "FlowViews::driveView")
 	id := ids(t, r)
 	edge := func(from, to string) string { return id[from] + "->" + id[to] }
@@ -1320,7 +1320,7 @@ func TestDebugActionSession(t *testing.T) {
 // An action that fails at a step reports the failure; a run that exceeds its
 // budget does too, as a failure rather than a hang.
 func TestDebugActionFailure(t *testing.T) {
-	s, docURI, _ := debugServer(t, "/w/f.sysml", `package Flows {
+	s, docURI, _ := debugServer(t, "f.sysml", `package Flows {
 	private import ScalarValues::*;
 	action def Spin {
 		attribute n : Integer = 0;
@@ -1372,7 +1372,7 @@ package FlowViews {
 // An edit leaving the behavior, performer and view as they were moves the session
 // to the fresh IDs, announced by debugChanged; one to the behavior ends it.
 func TestDebugSessionFollowsEdits(t *testing.T) {
-	s, docURI, rec := debugServer(t, "/w/m.sysml", debugMachine)
+	s, docURI, rec := debugServer(t, "m.sysml", debugMachine)
 	ctx := context.Background()
 	name := uriToName(docURI)
 	r := render(t, s, docURI, "MachineViews::opsView")
@@ -1441,7 +1441,7 @@ func TestDebugSessionFollowsEdits(t *testing.T) {
 // flight finishes at the documents it began with and the next one finds the
 // session already moved to the edited ones.
 func TestDebugEditWaitsForTheRequestInFlight(t *testing.T) {
-	s, docURI, rec := debugServer(t, "/w/m.sysml", debugMachine)
+	s, docURI, rec := debugServer(t, "m.sysml", debugMachine)
 	name := uriToName(docURI)
 	session := mustDebug(t, s, MethodDebugStart, &debugStartParams{
 		TextDocument: protocol.TextDocumentIdentifier{URI: docURI},
@@ -1477,7 +1477,7 @@ func TestDebugEditWaitsForTheRequestInFlight(t *testing.T) {
 // Every snapshot of a session, answered or notified, takes the next revision, so
 // a client can tell the newer of two that arrive out of order.
 func TestDebugSnapshotsAreNumbered(t *testing.T) {
-	s, docURI, rec := debugServer(t, "/w/m.sysml", debugMachine)
+	s, docURI, rec := debugServer(t, "m.sysml", debugMachine)
 	snap := mustDebug(t, s, MethodDebugStart, &debugStartParams{
 		TextDocument: protocol.TextDocumentIdentifier{URI: docURI},
 		View:         "MachineViews::opsView", Target: "Machines::Ops", Object: "Machines::Robot",
@@ -1520,7 +1520,7 @@ func TestDebugSnapshotsAreNumbered(t *testing.T) {
 // a machine and for an action paused in a nested flow alike.
 func TestDebugPauseFollowsEdits(t *testing.T) {
 	t.Run("machine", func(t *testing.T) {
-		s, docURI, rec := debugServer(t, "/w/m.sysml", debugMachine)
+		s, docURI, rec := debugServer(t, "m.sysml", debugMachine)
 		id := ids(t, render(t, s, docURI, "#state"))
 		snap := mustDebug(t, s, MethodDebugStart, &debugStartParams{
 			TextDocument: protocol.TextDocumentIdentifier{URI: docURI},
@@ -1559,7 +1559,7 @@ func TestDebugPauseFollowsEdits(t *testing.T) {
 		wantStrings(t, "active after resuming", snap.ActiveStates, []string{fresh["motion"], fresh["busy"], fresh["working"], fresh["clock"], fresh["waiting"]})
 	})
 	t.Run("action", func(t *testing.T) {
-		s, docURI, rec := debugServer(t, "/w/f.sysml", debugFlow)
+		s, docURI, rec := debugServer(t, "f.sysml", debugFlow)
 		id := ids(t, render(t, s, docURI, "#action"))
 		snap := mustDebug(t, s, MethodDebugStart, &debugStartParams{
 			TextDocument: protocol.TextDocumentIdentifier{URI: docURI}, View: "#action", Target: "Flows::Drive",
@@ -1602,7 +1602,7 @@ func TestDebugPauseFollowsEdits(t *testing.T) {
 // session to the fresh IDs before it answers; one to the behavior — of the same
 // length, so every span stays put — refuses the start.
 func TestDebugStartSeesAnEditSinceItsReading(t *testing.T) {
-	s, docURI, rec := debugServer(t, "/w/m.sysml", debugMachine)
+	s, docURI, rec := debugServer(t, "m.sysml", debugMachine)
 	ctx := context.Background()
 	name := uriToName(docURI)
 	params := &debugStartParams{
@@ -1692,7 +1692,7 @@ func TestDebugSessionEnds(t *testing.T) {
 	}
 
 	t.Run("performer edited", func(t *testing.T) {
-		s, docURI, rec := debugServer(t, "/w/m.sysml", debugMachine)
+		s, docURI, rec := debugServer(t, "m.sysml", debugMachine)
 		session := start(t, s, docURI)
 		s.applyDidChange(ctx, uriToName(docURI), []rawContentChange{{Text: strings.Replace(debugMachine, "exhibit state ops : Ops;", "exhibit state ops : Ops;\n\t\tattribute id : Integer;", 1)}}, 2)
 		if reason := lastEnd(t, rec, session).Reason; !strings.Contains(reason, "Machines::Robot was edited") {
@@ -1700,7 +1700,7 @@ func TestDebugSessionEnds(t *testing.T) {
 		}
 	})
 	t.Run("view removed", func(t *testing.T) {
-		s, docURI, rec := debugServer(t, "/w/m.sysml", debugMachine)
+		s, docURI, rec := debugServer(t, "m.sysml", debugMachine)
 		session := start(t, s, docURI)
 		s.applyDidChange(ctx, uriToName(docURI), []rawContentChange{{Text: strings.Replace(debugMachine, "view opsView : StateTransitionView { expose Machines::Ops; }", "", 1)}}, 2)
 		if reason := lastEnd(t, rec, session).Reason; !strings.Contains(reason, "MachineViews::opsView") {
@@ -1708,7 +1708,7 @@ func TestDebugSessionEnds(t *testing.T) {
 		}
 	})
 	t.Run("view rewritten but still drawing the target", func(t *testing.T) {
-		s, docURI, rec := debugServer(t, "/w/m.sysml", debugMachine)
+		s, docURI, rec := debugServer(t, "m.sysml", debugMachine)
 		session := start(t, s, docURI)
 		s.applyDidChange(ctx, uriToName(docURI), []rawContentChange{{Text: strings.Replace(debugMachine, "{ expose Machines::Ops; }", "{ expose Machines::Ops; expose Machines::Robot; }", 1)}}, 2)
 		if reason := lastEnd(t, rec, session).Reason; !strings.Contains(reason, "MachineViews::opsView was edited") {
@@ -1716,7 +1716,7 @@ func TestDebugSessionEnds(t *testing.T) {
 		}
 	})
 	t.Run("pseudo-view outlives edits around the target", func(t *testing.T) {
-		s, docURI, rec := debugServer(t, "/w/m.sysml", debugMachine)
+		s, docURI, rec := debugServer(t, "m.sysml", debugMachine)
 		snap := mustDebug(t, s, MethodDebugStart, &debugStartParams{
 			TextDocument: protocol.TextDocumentIdentifier{URI: docURI}, View: "#state:Machines::Ops", Target: "Machines::Ops",
 		})
@@ -1731,7 +1731,7 @@ func TestDebugSessionEnds(t *testing.T) {
 		}
 	})
 	t.Run("document closed", func(t *testing.T) {
-		s, docURI, rec := debugServer(t, "/w/m.sysml", debugMachine)
+		s, docURI, rec := debugServer(t, "m.sysml", debugMachine)
 		session := start(t, s, docURI)
 		if err := s.DidClose(ctx, &protocol.DidCloseTextDocumentParams{TextDocument: protocol.TextDocumentIdentifier{URI: docURI}}); err != nil {
 			t.Fatal(err)
@@ -1762,7 +1762,7 @@ func TestDebugSessionEnds(t *testing.T) {
 		}
 	})
 	t.Run("server shut down", func(t *testing.T) {
-		s, docURI, rec := debugServer(t, "/w/m.sysml", debugMachine)
+		s, docURI, rec := debugServer(t, "m.sysml", debugMachine)
 		first, second := start(t, s, docURI), start(t, s, docURI)
 		if err := s.Shutdown(ctx); err != nil {
 			t.Fatal(err)
@@ -1850,7 +1850,7 @@ func TestDebugSessionEndsWhenInheritedContentChanges(t *testing.T) {
 	}
 	for _, tc := range cases {
 		t.Run(tc.name, func(t *testing.T) {
-			s, docURI, rec := debugServer(t, "/w/i.sysml", debugDerived)
+			s, docURI, rec := debugServer(t, "i.sysml", debugDerived)
 			snap := mustDebug(t, s, MethodDebugStart, &debugStartParams{
 				TextDocument: protocol.TextDocumentIdentifier{URI: docURI}, View: tc.view, Target: tc.target,
 			})
@@ -1865,7 +1865,7 @@ func TestDebugSessionEndsWhenInheritedContentChanges(t *testing.T) {
 	}
 
 	// An edit elsewhere in the definition's package leaves the session running.
-	s, docURI, rec := debugServer(t, "/w/i.sysml", debugDerived)
+	s, docURI, rec := debugServer(t, "i.sysml", debugDerived)
 	snap := mustDebug(t, s, MethodDebugStart, &debugStartParams{
 		TextDocument: protocol.TextDocumentIdentifier{URI: docURI}, View: "InheritedViews::derivedView", Target: "Inherited::Sub::Derived",
 	})
@@ -1876,82 +1876,6 @@ func TestDebugSessionEndsWhenInheritedContentChanges(t *testing.T) {
 	}
 }
 
-// A view debugs the behavior it exposes from another document, performed by an
-// object from a third; edits there move or end the session, duplicates are refused.
-func TestDebugTargetDeclaredInAnotherDocument(t *testing.T) {
-	ctx := context.Background()
-	split := strings.Index(debugMachine, "package MachineViews")
-	machines, views := debugMachine[:split], debugMachine[split:]
-	open := func(t *testing.T, s *Server, name, src string) uri.URI {
-		t.Helper()
-		docURI := uri.File(name)
-		if err := s.DidOpen(ctx, &protocol.DidOpenTextDocumentParams{
-			TextDocument: protocol.TextDocumentItem{URI: docURI, LanguageID: "sysml", Version: 1, Text: src},
-		}); err != nil {
-			t.Fatalf("DidOpen %s: %v", name, err)
-		}
-		return docURI
-	}
-	s, viewsURI, rec := debugServer(t, "/w/views.sysml", views)
-	machinesURI := open(t, s, "/w/machines.sysml", machines)
-	open(t, s, "/w/robots.sysml", "package Robots { part def Rover { exhibit state ops : Machines::Ops; } }\n")
-	r := render(t, s, viewsURI, "MachineViews::opsView")
-	id := ids(t, r)
-
-	snap := mustDebug(t, s, MethodDebugStart, &debugStartParams{
-		TextDocument: protocol.TextDocumentIdentifier{URI: viewsURI},
-		View:         "MachineViews::opsView", Target: "Machines::Ops", Object: "Robots::Rover",
-	})
-	if snap.Target != "Machines::Ops" || snap.Object != "Robots::Rover" || snap.Root != r.Nodes[0].ID {
-		t.Fatalf("start snapshot = %s", describe(snap))
-	}
-	wantState(t, snap, debugWaiting)
-	wantStrings(t, "initial active states", snap.ActiveStates, []string{id["motion"], id["idle"], id["clock"], id["waiting"]})
-
-	// An edit to the machine's document that leaves the machine as declared
-	// keeps the session running; one rewriting the machine ends it.
-	s.applyDidChange(ctx, uriToName(machinesURI), []rawContentChange{{Text: strings.Replace(machines, "attribute def Halt;", "attribute def Halt;\n\tattribute def Stop;", 1)}}, 2)
-	for _, moved := range rec.debugChanged() {
-		if moved.Session != snap.Session || moved.State == debugEnded {
-			t.Fatalf("debugChanged after an unrelated edit to the machine's document = %s", describe(moved))
-		}
-		wantStrings(t, "active states after an unrelated edit", moved.ActiveStates, snap.ActiveStates)
-	}
-	s.applyDidChange(ctx, uriToName(machinesURI), []rawContentChange{{Text: strings.Replace(machines, "state elapsed;", "state elapsed;\n\t\tstate cooling;", 1)}}, 3)
-	changed := rec.debugChanged()
-	last := changed[len(changed)-1]
-	if last.Session != snap.Session || last.State != debugEnded || !strings.Contains(last.Reason, "Machines::Ops was edited") {
-		t.Fatalf("debugChanged after the machine was edited = %s", describe(last))
-	}
-
-	// Closing the machine's document ends a session on it too.
-	snap = mustDebug(t, s, MethodDebugStart, &debugStartParams{
-		TextDocument: protocol.TextDocumentIdentifier{URI: viewsURI}, View: "MachineViews::opsView", Target: "Machines::Ops",
-	})
-	if err := s.DidClose(ctx, &protocol.DidCloseTextDocumentParams{TextDocument: protocol.TextDocumentIdentifier{URI: machinesURI}}); err != nil {
-		t.Fatalf("DidClose: %v", err)
-	}
-	changed = rec.debugChanged()
-	last = changed[len(changed)-1]
-	if last.Session != snap.Session || last.State != debugEnded || !strings.Contains(last.Reason, "machines.sysml was closed") {
-		t.Fatalf("debugChanged after closing the machine's document = %s", describe(last))
-	}
-
-	// The same name declared by two documents names neither.
-	open(t, s, "/w/machines.sysml", machines)
-	open(t, s, "/w/spare.sysml", machines)
-	_, err := s.DebugStart(&debugStartParams{
-		TextDocument: protocol.TextDocumentIdentifier{URI: viewsURI}, View: "MachineViews::opsView", Target: "Machines::Ops",
-	})
-	if !errors.Is(err, ErrDebugTarget) || !strings.Contains(err.Error(), "/w/machines.sysml, /w/spare.sysml") {
-		t.Fatalf("start of an ambiguous target: err = %v, want %v naming both documents", err, ErrDebugTarget)
-	}
-	var wire *jsonrpc2.Error
-	if !errors.As(err, &wire) || wire.Code != jsonrpc2.InvalidParams {
-		t.Errorf("err = %v, want an InvalidParams reply", err)
-	}
-}
-
 // Closing the target's or the object's document ends a session even when the
 // file is on disk, so the workspace goes on holding the document it declares.
 func TestDebugEndsWhenTargetOrObjectDocumentClosedOnDisk(t *testing.T) {
@@ -2082,7 +2006,7 @@ func TestDebugSessionEndsWhenWhatItReadsChanges(t *testing.T) {
 	}
 	for _, tc := range cases {
 		t.Run(tc.name, func(t *testing.T) {
-			s, docURI, rec := debugServer(t, "/w/d.sysml", debugReads)
+			s, docURI, rec := debugServer(t, "d.sysml", debugReads)
 			snap := mustDebug(t, s, MethodDebugStart, &debugStartParams{
 				TextDocument: protocol.TextDocumentIdentifier{URI: docURI}, View: tc.view, Target: tc.target, Object: tc.object,
 			})
@@ -2097,7 +2021,7 @@ func TestDebugSessionEndsWhenWhatItReadsChanges(t *testing.T) {
 	}
 
 	t.Run("signal a bare trigger names", func(t *testing.T) {
-		s, docURI, rec := debugServer(t, "/w/m.sysml", debugMachine)
+		s, docURI, rec := debugServer(t, "m.sysml", debugMachine)
 		snap := mustDebug(t, s, MethodDebugStart, &debugStartParams{
 			TextDocument: protocol.TextDocumentIdentifier{URI: docURI}, View: "MachineViews::opsView", Target: "Machines::Ops",
 		})
@@ -2109,7 +2033,7 @@ func TestDebugSessionEndsWhenWhatItReadsChanges(t *testing.T) {
 	})
 
 	t.Run("value a send named", func(t *testing.T) {
-		s, docURI, rec := debugServer(t, "/w/d.sysml", debugReads)
+		s, docURI, rec := debugServer(t, "d.sysml", debugReads)
 		snap := mustDebug(t, s, MethodDebugStart, &debugStartParams{
 			TextDocument: protocol.TextDocumentIdentifier{URI: docURI}, View: "DepViews::opsView", Target: "Deps::Ops",
 		})
@@ -2128,7 +2052,7 @@ func TestDebugSessionEndsWhenWhatItReadsChanges(t *testing.T) {
 			t.Errorf("step after the end: %v, want %v", err, ErrDebugSession)
 		}
 
-		s, docURI, rec = debugServer(t, "/w/d.sysml", debugReads)
+		s, docURI, rec = debugServer(t, "d.sysml", debugReads)
 		snap = mustDebug(t, s, MethodDebugStart, &debugStartParams{
 			TextDocument: protocol.TextDocumentIdentifier{URI: docURI}, View: "DepViews::opsView", Target: "Deps::Ops",
 		})
@@ -2155,7 +2079,7 @@ func TestDebugSessionEndsWhenWhatItReadsChanges(t *testing.T) {
 	}
 	for _, tc := range unread {
 		t.Run(tc.name, func(t *testing.T) {
-			s, docURI, rec := debugServer(t, "/w/d.sysml", debugReads)
+			s, docURI, rec := debugServer(t, "d.sysml", debugReads)
 			snap := mustDebug(t, s, MethodDebugStart, &debugStartParams{
 				TextDocument: protocol.TextDocumentIdentifier{URI: docURI}, View: "DepViews::opsView", Target: "Deps::Ops", Object: "Deps::Bots::Robot",
 			})
@@ -2175,7 +2099,7 @@ func TestDebugSessionEndsWhenWhatItReadsChanges(t *testing.T) {
 // Sessions run in runtimes of their own: two over one machine do not share
 // state, and rendering the view they draw on is unchanged by their running.
 func TestDebugSessionsAreIsolated(t *testing.T) {
-	s, docURI, _ := debugServer(t, "/w/m.sysml", debugMachine)
+	s, docURI, _ := debugServer(t, "m.sysml", debugMachine)
 	plain := render(t, s, docURI, "MachineViews::opsView")
 	params := &debugStartParams{
 		TextDocument: protocol.TextDocumentIdentifier{URI: docURI},
diff --git a/internal/frontend/lsp/handler_test.go b/internal/frontend/lsp/handler_test.go
index 6f2361d314..9d389545b7 100644
--- a/internal/frontend/lsp/handler_test.go
+++ b/internal/frontend/lsp/handler_test.go
@@ -12,13 +12,12 @@ import (
 	"time"
 
 	"github.com/Open-MBEE/OpenSysML/internal/workspace/model"
+	"go.lsp.dev/uri"
 )
 
 // These tests drive textDocument/didChange with the framed JSON an editor sends,
 // where an omitted range (full replace) and a {0,0}-{0,0} range (insert) differ.
 
-const wireURI = "file:///tmp/wire.sysml"
-
 const wireSource = "package Vehicles {\n    part def Wheel;\n    part w : Wheel;\n}\n"
 
 // wireSession is a served Server reached only through its framed stream;
@@ -26,6 +25,7 @@ const wireSource = "package Vehicles {\n    part def Wheel;\n    part w : Wheel;
 type wireSession struct {
 	t       *testing.T
 	s       *Server
+	uri     string
 	client  net.Conn
 	msgs    chan map[string]any
 	readErr chan error
@@ -55,6 +55,7 @@ func newWireSession(t *testing.T) *wireSession {
 	w := &wireSession{
 		t:       t,
 		s:       s,
+		uri:     string(tempDocURI(t, "wire.sysml")),
 		client:  client,
 		msgs:    make(chan map[string]any, 256),
 		readErr: make(chan error, 1),
@@ -155,42 +156,42 @@ func (w *wireSession) next(what string, want func(map[string]any) bool) map[stri
 	}
 }
 
-// open initializes the session and opens wireURI with text, consuming its diagnostics.
+// open initializes the session and opens w.uri with text, consuming its diagnostics.
 func (w *wireSession) open(text string) {
 	w.t.Helper()
 	w.call("initialize", `{"capabilities":{}}`)
 	w.notify("initialized", `{}`)
 	w.notify("textDocument/didOpen", fmt.Sprintf(
-		`{"textDocument":{"uri":%q,"languageId":"sysml","version":1,"text":%s}}`, wireURI, jsonString(text)))
-	if diags := w.awaitDiagnostics(wireURI); len(diags) != 0 {
+		`{"textDocument":{"uri":%q,"languageId":"sysml","version":1,"text":%s}}`, w.uri, jsonString(text)))
+	if diags := w.awaitDiagnostics(w.uri); len(diags) != 0 {
 		w.t.Fatalf("didOpen published %v, want a clean document to start from", diags)
 	}
 }
 
-// didChange sends the given JSON change objects verbatim for wireURI and
+// didChange sends the given JSON change objects verbatim for w.uri and
 // returns the diagnostics published for the result.
 func (w *wireSession) didChange(version int, changes ...string) []any {
 	w.t.Helper()
 	w.notify("textDocument/didChange", fmt.Sprintf(
 		`{"textDocument":{"uri":%q,"version":%d},"contentChanges":[%s]}`,
-		wireURI, version, strings.Join(changes, ",")))
-	return w.awaitDiagnostics(wireURI)
+		w.uri, version, strings.Join(changes, ",")))
+	return w.awaitDiagnostics(w.uri)
 }
 
-// content is the text the workspace holds for wireURI.
+// content is the text the workspace holds for w.uri.
 func (w *wireSession) content() string {
 	w.t.Helper()
-	doc := w.s.ws.Document(uriToName(wireURI))
+	doc := w.s.ws.Document(uriToName(uri.URI(w.uri)))
 	if doc == nil {
-		w.t.Fatalf("%s is not in the workspace", wireURI)
+		w.t.Fatalf("%s is not in the workspace", w.uri)
 	}
 	return string(doc.Content)
 }
 
-// symbolNames returns the top-level documentSymbol names of wireURI.
+// symbolNames returns the top-level documentSymbol names of w.uri.
 func (w *wireSession) symbolNames() []string {
 	w.t.Helper()
-	result := w.call("textDocument/documentSymbol", fmt.Sprintf(`{"textDocument":{"uri":%q}}`, wireURI))
+	result := w.call("textDocument/documentSymbol", fmt.Sprintf(`{"textDocument":{"uri":%q}}`, w.uri))
 	symbols, ok := result.([]any)
 	if !ok {
 		w.t.Fatalf("documentSymbol result = %v, want an array", result)
@@ -208,7 +209,7 @@ func (w *wireSession) symbolNames() []string {
 func (w *wireSession) hoverText(line, character int) string {
 	w.t.Helper()
 	result := w.call("textDocument/hover", fmt.Sprintf(
-		`{"textDocument":{"uri":%q},"position":{"line":%d,"character":%d}}`, wireURI, line, character))
+		`{"textDocument":{"uri":%q},"position":{"line":%d,"character":%d}}`, w.uri, line, character))
 	if result == nil {
 		return ""
 	}
@@ -319,7 +320,7 @@ func TestWireDidChangeMixedBatchAppliesInOrder(t *testing.T) {
 	if got := w.content(); got != want {
 		t.Errorf("content = %q, want %q", got, want)
 	}
-	result := w.call("textDocument/documentSymbol", fmt.Sprintf(`{"textDocument":{"uri":%q}}`, wireURI))
+	result := w.call("textDocument/documentSymbol", fmt.Sprintf(`{"textDocument":{"uri":%q}}`, w.uri))
 	symbols, _ := result.([]any)
 	if len(symbols) != 1 {
 		t.Fatalf("documentSymbol = %v, want the one package Final", result)
@@ -384,7 +385,7 @@ func TestWireRangeFormattingAnswersEditsOnSelectedLines(t *testing.T) {
 	request := func(startLine, endLine int) []any {
 		result := w.call("textDocument/rangeFormatting", fmt.Sprintf(
 			`{"textDocument":{"uri":%q},"range":{"start":{"line":%d,"character":0},"end":{"line":%d,"character":0}},"options":{"tabSize":4,"insertSpaces":true}}`,
-			wireURI, startLine, endLine))
+			w.uri, startLine, endLine))
 		if result == nil {
 			return nil
 		}
diff --git a/internal/frontend/lsp/integration_test.go b/internal/frontend/lsp/integration_test.go
index 6904fbaf00..e0b99709f7 100644
--- a/internal/frontend/lsp/integration_test.go
+++ b/internal/frontend/lsp/integration_test.go
@@ -6,7 +6,6 @@ import (
 	"testing"
 
 	"go.lsp.dev/protocol"
-	"go.lsp.dev/uri"
 
 	"github.com/Open-MBEE/OpenSysML/internal/workspace/model"
 )
@@ -29,9 +28,8 @@ func TestLSPEndToEnd(t *testing.T) {
 	}
 
 	// Open a document.
-	name := "e2e.sysml"
 	src := "package P { namespace N; }\nimport P::N;\n"
-	docURI := uri.File(name)
+	docURI := tempDocURI(t, "e2e.sysml")
 	if err := s.DidOpen(ctx, &protocol.DidOpenTextDocumentParams{
 		TextDocument: protocol.TextDocumentItem{
 			URI:        docURI,
diff --git a/internal/frontend/lsp/modeledit_cross_document_test.go b/internal/frontend/lsp/modeledit_cross_document_test.go
index 12d4951eb1..97483a9322 100644
--- a/internal/frontend/lsp/modeledit_cross_document_test.go
+++ b/internal/frontend/lsp/modeledit_cross_document_test.go
@@ -21,7 +21,7 @@ const (
 func engineWorkspace(t *testing.T) (s *Server, viewsURI, partsURI uri.URI) {
 	t.Helper()
 	s, viewsURI = renderServer(t, "views.sysml", engineViews)
-	partsURI = uri.File("parts.sysml")
+	partsURI = tempDocURI(t, "parts.sysml")
 	openDoc(t, s, partsURI, engineParts)
 	return s, viewsURI, partsURI
 }
@@ -93,7 +93,7 @@ func TestRenderLocatesNodesInTheDocumentDeclaringThem(t *testing.T) {
 func TestRenderMarksWhatEachDocumentsNodesAdmit(t *testing.T) {
 	const views = "package EngineViews {\n\tprivate import Views::*;\n\tprivate import StandardViewDefinitions::*;\n\n\tpart def Mount;\n\tview engineView : InterconnectionView {\n\t\texpose Mount;\n\t\texpose Machinery::Engine;\n\t\texpose Parts::Part;\n\t}\n}\n"
 	s, viewsURI := renderServer(t, "views.sysml", views)
-	partsURI := uri.File("parts.sysml")
+	partsURI := tempDocURI(t, "parts.sysml")
 	openDoc(t, s, partsURI, engineParts)
 	drawn := render(t, s, viewsURI, "EngineViews::engineView")
 
@@ -137,7 +137,7 @@ func TestRenderMarksWhatEachDocumentsNodesAdmit(t *testing.T) {
 func TestRenderNamesOnlyTheRequestedDocumentsDeclarationsToAClientWithoutTheCapability(t *testing.T) {
 	const views = "package EngineViews {\n\tprivate import Views::*;\n\tprivate import StandardViewDefinitions::*;\n\n\tpart def Mount;\n\tview engineView : InterconnectionView {\n\t\texpose Mount;\n\t\texpose Machinery::Engine;\n\t}\n}\n"
 	s := initializedServer(t, nil)
-	viewsURI, partsURI := uri.File("views.sysml"), uri.File("parts.sysml")
+	viewsURI, partsURI := tempDocURI(t, "views.sysml"), tempDocURI(t, "parts.sysml")
 	openDoc(t, s, viewsURI, views)
 	openDoc(t, s, partsURI, engineParts)
 	drawn := render(t, s, viewsURI, "EngineViews::engineView")
@@ -296,7 +296,7 @@ func TestApplyModelEditPlacesInlineIntoTheDeclaringDocument(t *testing.T) {
 	const motor = "package Motors {\n\tstate def Motor {\n\t\tstate off;\n\t\tstate on;\n\t\ttransition first off then on;\n\t}\n}\n"
 	const fleet = "package Fleet {\n\tstate motor : Motors::Motor;\n}\n"
 	s, fleetURI := renderServer(t, "fleet.sysml", fleet)
-	motorURI := uri.File("motor.sysml")
+	motorURI := tempDocURI(t, "motor.sysml")
 	openDoc(t, s, motorURI, motor)
 	tellChanged(t, s, motorURI, motor, 2)
 
@@ -413,7 +413,7 @@ func TestApplyModelEditLayoutIntoDiskAndLibraryDocuments(t *testing.T) {
 func TestApplyModelEditLayoutRefusesWhenAnotherDocumentBecomesInvalid(t *testing.T) {
 	shadowed := strings.Replace(engineViews, "\tview engineView", "\tpart def DiagramLayout;\n\tview engineView", 1)
 	s, partsURI := renderServer(t, "parts.sysml", engineParts)
-	viewsURI := uri.File("views.sysml")
+	viewsURI := tempDocURI(t, "views.sysml")
 	openDoc(t, s, viewsURI, shadowed)
 
 	out := applyModelEdit(t, s, partsURI, 1,
diff --git a/internal/frontend/lsp/modeledit_test.go b/internal/frontend/lsp/modeledit_test.go
index e48047d430..500ab8314a 100644
--- a/internal/frontend/lsp/modeledit_test.go
+++ b/internal/frontend/lsp/modeledit_test.go
@@ -513,7 +513,7 @@ func TestApplyModelEditRefusesImpossibleMoves(t *testing.T) {
 		t.Errorf("clashing move = %+v, want member-name-taken", out)
 	}
 	s, docURI = renderServer(t, "vehicle.sysml", editModel)
-	fleetURI := uri.File("fleet.sysml")
+	fleetURI := tempDocURI(t, "fleet.sysml")
 	openDoc(t, s, fleetURI, "package Fleet {\n    part truck : Vehicle::Car;\n}\n")
 	out = applyModelEdit(t, s, docURI, 1, ModelEditOperation{Kind: EditMove, Target: "Vehicle::Car", Owner: "Vehicle::Tank"})
 	if len(out.Refused) != 1 || out.Refused[0].Failure != "referenced-elsewhere" {
@@ -553,7 +553,7 @@ const fleetModel = "package Fleet {\n    part truck : Vehicle::Car;\n    part va
 // the version the server holds for it.
 func TestApplyModelEditRenameRespellsAnotherDocument(t *testing.T) {
 	s, docURI := renderServer(t, "vehicle.sysml", editModel)
-	fleetURI := uri.File("fleet.sysml")
+	fleetURI := tempDocURI(t, "fleet.sysml")
 	openDoc(t, s, fleetURI, fleetModel)
 	op := ModelEditOperation{Kind: EditRename, Target: "Vehicle::Car", NewName: "Auto"}
 	out := applyModelEdit(t, s, docURI, 1, op)
@@ -581,7 +581,7 @@ func TestApplyModelEditRenameRespellsAnotherDocument(t *testing.T) {
 // without cascade it is refused, naming them by document.
 func TestApplyModelEditDeleteCascadesIntoAnotherDocument(t *testing.T) {
 	s, docURI := renderServer(t, "vehicle.sysml", editModel)
-	fleetURI := uri.File("fleet.sysml")
+	fleetURI := tempDocURI(t, "fleet.sysml")
 	openDoc(t, s, fleetURI, fleetModel)
 
 	out := applyModelEdit(t, s, docURI, 1, ModelEditOperation{Kind: EditDelete, Target: "Vehicle::Car"})
@@ -622,7 +622,7 @@ func TestApplyModelEditDeleteCascadesIntoAnotherDocument(t *testing.T) {
 // document read from disk, which no client versions, carries none.
 func TestApplyModelEditVersionsOtherDocumentsAsHeld(t *testing.T) {
 	s, docURI := renderServer(t, "vehicle.sysml", editModel)
-	fleetURI := uri.File("fleet.sysml")
+	fleetURI := tempDocURI(t, "fleet.sysml")
 	openDoc(t, s, fleetURI, fleetModel)
 	sendDidChange(t, s, fleetURI, 3, []json.RawMessage{json.RawMessage(`{"text":"package Fleet {\n    part van : Vehicle::Car;\n}\n"}`)})
 	depotName := uri.File("depot.sysml").Filename()
diff --git a/internal/frontend/lsp/opened_directory_test.go b/internal/frontend/lsp/opened_directory_test.go
new file mode 100644
index 0000000000..f070b14b12
--- /dev/null
+++ b/internal/frontend/lsp/opened_directory_test.go
@@ -0,0 +1,108 @@
+package lsp
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"go.lsp.dev/protocol"
+	"go.lsp.dev/uri"
+
+	"github.com/Open-MBEE/OpenSysML/internal/workspace/model"
+)
+
+// A document opened under no folder has its own directory indexed and nothing
+// above it: a model file in the parent directory stays out of the workspace.
+func TestOpenedDocumentIndexesOnlyItsOwnDirectory(t *testing.T) {
+	root := t.TempDir()
+	stray := filepath.Join(root, "stray.sysml")
+	if err := os.WriteFile(stray, []byte("package Stray;\n"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	dir := filepath.Join(root, "proj")
+	if err := os.MkdirAll(dir, 0o750); err != nil {
+		t.Fatal(err)
+	}
+	sibling := filepath.Join(dir, "sibling.sysml")
+	if err := os.WriteFile(sibling, []byte("package Sibling;\n"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+
+	s := NewServer(model.NewWorkspace())
+	docURI := uri.File(filepath.Join(dir, "doc.sysml"))
+	openDoc(t, s, docURI, "package P;\n")
+
+	names := s.ws.DocumentNames()
+	if !containsName(names, sibling) {
+		t.Errorf("sibling %s not indexed; documents = %v", sibling, names)
+	}
+	if containsName(names, stray) {
+		t.Errorf("%s in the parent directory was indexed; documents = %v", stray, names)
+	}
+	if len(s.openDirs) != 1 || !s.openDirs[dir] {
+		t.Errorf("indexed directories = %v, want only %s", s.openDirs, dir)
+	}
+}
+
+// Every helper that opens a document places it under the test's root: a stray
+// model file in the system temp directory is never indexed, nor any directory outside.
+func TestOpenHelpersStayUnderTheTestRoot(t *testing.T) {
+	stray := filepath.Join(os.TempDir(), "opensysml-lsp-stray-guard.sysml")
+	if err := os.WriteFile(stray, []byte("package OpenSysMLStrayGuard;\n"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { _ = os.Remove(stray) })
+	testRoot := filepath.Dir(t.TempDir())
+
+	const src = "package P { part def Wheel; }\n"
+	check := func(what string, s *Server) {
+		t.Helper()
+		if names := s.ws.DocumentNames(); containsName(names, stray) {
+			t.Errorf("%s indexed %s outside the test root; documents = %v", what, stray, names)
+		}
+		if len(s.openDirs) == 0 {
+			t.Errorf("%s indexed no directory for the document it opened", what)
+		}
+		for dir := range s.openDirs {
+			if !underFolder(dir, testRoot) {
+				t.Errorf("%s indexed %s, outside the test root %s", what, dir, testRoot)
+			}
+		}
+	}
+
+	w := newWireSession(t)
+	w.open(src)
+	if !strings.HasPrefix(uriToName(uri.URI(w.uri)), testRoot+string(filepath.Separator)) {
+		t.Errorf("wire session document %s is outside the test root %s", w.uri, testRoot)
+	}
+	check("wireSession.open", w.s)
+
+	s := NewServer(model.NewWorkspace())
+	openDoc(t, s, tempDocURI(t, "a.sysml"), src)
+	check("openDoc(tempDocURI)", s)
+
+	s, _ = renderServer(t, "kit.sysml", src)
+	check("renderServer", s)
+
+	s, _, _ = debugServer(t, "m.sysml", src)
+	check("debugServer", s)
+
+	s = NewServer(model.NewWorkspace())
+	if err := s.DidOpen(context.Background(), &protocol.DidOpenTextDocumentParams{
+		TextDocument: protocol.TextDocumentItem{URI: tempDocURI(t, "b.sysml"), LanguageID: "sysml", Version: 1, Text: src},
+	}); err != nil {
+		t.Fatalf("DidOpen err = %v", err)
+	}
+	check("DidOpen(tempDocURI)", s)
+}
+
+func containsName(names []string, name string) bool {
+	for _, n := range names {
+		if n == name {
+			return true
+		}
+	}
+	return false
+}
diff --git a/internal/frontend/lsp/protocol_editor_facts_test.go b/internal/frontend/lsp/protocol_editor_facts_test.go
index 10c24975bf..299d8018c3 100644
--- a/internal/frontend/lsp/protocol_editor_facts_test.go
+++ b/internal/frontend/lsp/protocol_editor_facts_test.go
@@ -21,7 +21,7 @@ func TestRunServesSignatureHelpCodeLensAndInlayHints(t *testing.T) {
 	done := make(chan error, 1)
 	go func() { done <- s.Run(context.Background(), server) }()
 
-	const file = "file:///tmp/protocol_editor_facts.sysml"
+	file := string(tempDocURI(t, "protocol_editor_facts.sysml"))
 	doc := map[string]any{"uri": file}
 	callPos := positionAfter(t, editorFactsModel, "fell = Fall(20.0, 9.")
 	lines := uint32(len(editorFactsModel))
diff --git a/internal/frontend/lsp/protocol_features_test.go b/internal/frontend/lsp/protocol_features_test.go
index 12e91ad0c7..dfdaf68b16 100644
--- a/internal/frontend/lsp/protocol_features_test.go
+++ b/internal/frontend/lsp/protocol_features_test.go
@@ -24,7 +24,7 @@ func TestRunServesSemanticTokensAndCodeAction(t *testing.T) {
 	go func() { done <- s.Run(context.Background(), server) }()
 
 	const src = "package P {\n    part def Wheel;\n    part w : Wheeel;\n}\n"
-	const file = "file:///tmp/protocol_features.sysml"
+	file := string(tempDocURI(t, "protocol_features.sysml"))
 	doc := map[string]any{"uri": file}
 	requests := []map[string]any{
 		{"jsonrpc": "2.0", "id": 1, "method": "initialize",
diff --git a/internal/frontend/lsp/render_filter_test.go b/internal/frontend/lsp/render_filter_test.go
index 78e22e0c15..2e55b03b90 100644
--- a/internal/frontend/lsp/render_filter_test.go
+++ b/internal/frontend/lsp/render_filter_test.go
@@ -15,7 +15,7 @@ import (
 func TestRenderFiltersByAMetaclassDeclaredByTwoDocuments(t *testing.T) {
 	s := initializedServer(t, map[string]any{CrossDocumentCapability: true})
 	open := func(name, src string) uri.URI {
-		docURI := uri.File(name)
+		docURI := tempDocURI(t, name)
 		if err := s.DidOpen(context.Background(), &protocol.DidOpenTextDocumentParams{
 			TextDocument: protocol.TextDocumentItem{URI: docURI, LanguageID: "sysml", Version: 1, Text: src},
 		}); err != nil {
@@ -24,9 +24,9 @@ func TestRenderFiltersByAMetaclassDeclaredByTwoDocuments(t *testing.T) {
 		return docURI
 	}
 	const metaclassCopy = `package SysML { package Systems { metadata def PartUsage; } }`
-	open("/ws/lib_one.sysml", metaclassCopy)
-	open("/ws/lib_two.sysml", metaclassCopy)
-	docURI := open("/ws/interconnection.sysml", `
+	open("lib_one.sysml", metaclassCopy)
+	open("lib_two.sysml", metaclassCopy)
+	docURI := open("interconnection.sysml", `
 		package Model {
 			part abcd {
 				part a { port a; }
diff --git a/internal/frontend/lsp/render_test.go b/internal/frontend/lsp/render_test.go
index a0afd92680..5e7a510472 100644
--- a/internal/frontend/lsp/render_test.go
+++ b/internal/frontend/lsp/render_test.go
@@ -139,7 +139,7 @@ func (r *recorder) all() []string {
 func renderServer(t *testing.T, name, src string) (*Server, uri.URI) {
 	t.Helper()
 	s := initializedServer(t, map[string]any{CrossDocumentCapability: true})
-	docURI := uri.File(name)
+	docURI := testDocURI(t, name)
 	if err := s.DidOpen(context.Background(), &protocol.DidOpenTextDocumentParams{
 		TextDocument: protocol.TextDocumentItem{
 			URI: docURI, LanguageID: "sysml", Version: 1, Text: src,
@@ -1173,7 +1173,7 @@ func TestDidChangeNotifiesRenderChangedAfterDiagnostics(t *testing.T) {
 	s.client = rec
 	s.notifier = rec
 	ctx := context.Background()
-	docURI := uri.File("kit.sysml")
+	docURI := tempDocURI(t, "kit.sysml")
 	if err := s.DidOpen(ctx, &protocol.DidOpenTextDocumentParams{
 		TextDocument: protocol.TextDocumentItem{
 			URI: docURI, LanguageID: "sysml", Version: 1, Text: "package Kit {\n\tpart def Widget;\n}\n",
diff --git a/internal/frontend/lsp/run_test.go b/internal/frontend/lsp/run_test.go
index 9dfaed5ce1..9a62ca9c1d 100644
--- a/internal/frontend/lsp/run_test.go
+++ b/internal/frontend/lsp/run_test.go
@@ -122,6 +122,7 @@ func TestRunServesEveryRequestOverOneStream(t *testing.T) {
 	// Writes run concurrently with reads: net.Pipe is unbuffered, so the
 	// server's diagnostics notifications must be drained as they are sent.
 	const requests = 25
+	file := string(tempDocURI(t, "run.sysml"))
 	writeErr := make(chan error, 1)
 	go func() {
 		messages := []any{
@@ -133,7 +134,7 @@ func TestRunServesEveryRequestOverOneStream(t *testing.T) {
 			map[string]any{
 				"jsonrpc": "2.0", "method": "textDocument/didOpen",
 				"params": map[string]any{"textDocument": map[string]any{
-					"uri": "file:///tmp/run.sysml", "languageId": "sysml", "version": 1,
+					"uri": file, "languageId": "sysml", "version": 1,
 					"text": "package P {\n    part def Wheel { attribute pressure; }\n    part w : Wheel;\n}\n",
 				}},
 			},
@@ -142,7 +143,7 @@ func TestRunServesEveryRequestOverOneStream(t *testing.T) {
 			messages = append(messages, map[string]any{
 				"jsonrpc": "2.0", "id": id, "method": "textDocument/completion",
 				"params": map[string]any{
-					"textDocument": map[string]any{"uri": "file:///tmp/run.sysml"},
+					"textDocument": map[string]any{"uri": file},
 					"position":     map[string]any{"line": 2, "character": 18},
 				},
 			})
diff --git a/internal/frontend/lsp/stdlib_test.go b/internal/frontend/lsp/stdlib_test.go
index 1127b70ef8..316c8f4fbf 100644
--- a/internal/frontend/lsp/stdlib_test.go
+++ b/internal/frontend/lsp/stdlib_test.go
@@ -416,17 +416,18 @@ func TestRunServesLibraryDocumentsOverStream(t *testing.T) {
 	send(map[string]any{"jsonrpc": "2.0", "method": "initialized", "params": map[string]any{}})
 
 	src := "package P { attribute x : ScalarValues::Integer; }\n"
+	file := string(tempDocURI(t, "stream.sysml"))
 	send(map[string]any{
 		"jsonrpc": "2.0", "method": "textDocument/didOpen",
 		"params": map[string]any{"textDocument": map[string]any{
-			"uri": "file:///tmp/stream.sysml", "languageId": "sysml", "version": 1, "text": src,
+			"uri": file, "languageId": "sysml", "version": 1, "text": src,
 		}},
 	})
 	pos := offsetToPosition([]byte(src), strings.Index(src, "Integer"))
 	send(map[string]any{
 		"jsonrpc": "2.0", "id": 2, "method": "textDocument/definition",
 		"params": map[string]any{
-			"textDocument": map[string]any{"uri": "file:///tmp/stream.sysml"},
+			"textDocument": map[string]any{"uri": file},
 			"position":     map[string]any{"line": pos.Line, "character": pos.Character},
 		},
 	})
@@ -451,7 +452,7 @@ func TestRunServesLibraryDocumentsOverStream(t *testing.T) {
 		t.Errorf("%s returned %d bytes, want the bundled ScalarValues.kerml (%d bytes)", MethodStdlibContent, len(got), len(text))
 	}
 
-	send(map[string]any{"jsonrpc": "2.0", "id": 4, "method": MethodStdlibContent, "params": map[string]any{"uri": "file:///tmp/stream.sysml"}})
+	send(map[string]any{"jsonrpc": "2.0", "id": 4, "method": MethodStdlibContent, "params": map[string]any{"uri": file}})
 	res = await(4, nil)
 	if res["error"] == nil {
 		t.Errorf("%s on a file URI answered %v, want an error", MethodStdlibContent, res["result"])
diff --git a/internal/frontend/lsp/sync_test.go b/internal/frontend/lsp/sync_test.go
index 04500aa43a..9cf8a76868 100644
--- a/internal/frontend/lsp/sync_test.go
+++ b/internal/frontend/lsp/sync_test.go
@@ -15,7 +15,7 @@ import (
 
 func TestDidOpenRegistersDocument(t *testing.T) {
 	s := NewServer(model.NewWorkspace())
-	u := uri.File("/tmp/a.sysml")
+	u := tempDocURI(t, "a.sysml")
 	err := s.DidOpen(context.Background(), &protocol.DidOpenTextDocumentParams{
 		TextDocument: protocol.TextDocumentItem{
 			URI:     u,
@@ -60,6 +60,7 @@ func sendDidChange(t *testing.T, s *Server, u uri.URI, version int32, rawChanges
 
 func openDoc(t *testing.T, s *Server, u uri.URI, text string) {
 	t.Helper()
+	requireTestOwnedDir(t, u)
 	if err := s.DidOpen(context.Background(), &protocol.DidOpenTextDocumentParams{
 		TextDocument: protocol.TextDocumentItem{URI: u, Version: 1, Text: text},
 	}); err != nil {
@@ -69,7 +70,7 @@ func openDoc(t *testing.T, s *Server, u uri.URI, text string) {
 
 func TestDidChangeFullReplace(t *testing.T) {
 	s := NewServer(model.NewWorkspace())
-	u := uri.File("/tmp/a.sysml")
+	u := tempDocURI(t, "a.sysml")
 	openDoc(t, s, u, "package P;\n")
 	// A full-document replace omits "range" entirely.
 	sendDidChange(t, s, u, 2, []json.RawMessage{
@@ -82,7 +83,7 @@ func TestDidChangeFullReplace(t *testing.T) {
 
 func TestDidChangeIncremental(t *testing.T) {
 	s := NewServer(model.NewWorkspace())
-	u := uri.File("/tmp/a.sysml")
+	u := tempDocURI(t, "a.sysml")
 	openDoc(t, s, u, "package P;\n")
 	// Replace the single character 'P' (line 0, chars 8..9) with "Hello".
 	sendDidChange(t, s, u, 2, []json.RawMessage{
@@ -98,7 +99,7 @@ func TestDidChangeIncremental(t *testing.T) {
 // front instead of wiping the buffer.
 func TestDidChangeIncrementalInsertAtStart(t *testing.T) {
 	s := NewServer(model.NewWorkspace())
-	u := uri.File("/tmp/a.sysml")
+	u := tempDocURI(t, "a.sysml")
 	openDoc(t, s, u, "package P;\n")
 	sendDidChange(t, s, u, 2, []json.RawMessage{
 		json.RawMessage(`{"range":{"start":{"line":0,"character":0},"end":{"line":0,"character":0}},"text":"X"}`),
@@ -112,7 +113,7 @@ func TestDidChangeIncrementalInsertAtStart(t *testing.T) {
 // start must apply all edits sequentially against the accumulating buffer.
 func TestDidChangeMultiChangeStartingAtOffsetZero(t *testing.T) {
 	s := NewServer(model.NewWorkspace())
-	u := uri.File("/tmp/a.sysml")
+	u := tempDocURI(t, "a.sysml")
 	openDoc(t, s, u, "abc\n")
 	sendDidChange(t, s, u, 2, []json.RawMessage{
 		json.RawMessage(`{"range":{"start":{"line":0,"character":0},"end":{"line":0,"character":0}},"text":"X"}`),
@@ -127,7 +128,7 @@ func TestDidChangeMultiChangeStartingAtOffsetZero(t *testing.T) {
 // UTF-16 columns; the byte offset must skip the 4-byte emoji correctly.
 func TestDidChangeIncrementalAstral(t *testing.T) {
 	s := NewServer(model.NewWorkspace())
-	u := uri.File("/tmp/a.sysml")
+	u := tempDocURI(t, "a.sysml")
 	openDoc(t, s, u, "😀ab\n") // emoji = 2 UTF-16 units; 'a' at char 2, 'b' at char 3
 	// Replace 'a' (chars 2..3) with "Z".
 	sendDidChange(t, s, u, 2, []json.RawMessage{
diff --git a/internal/frontend/lsp/tempdoc_test.go b/internal/frontend/lsp/tempdoc_test.go
new file mode 100644
index 0000000000..76106dc0a2
--- /dev/null
+++ b/internal/frontend/lsp/tempdoc_test.go
@@ -0,0 +1,42 @@
+package lsp
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"go.lsp.dev/uri"
+)
+
+// tempDocURI names a document in a directory of the test's own, so opening it
+// under no folder indexes that directory and never a shared one such as /tmp.
+func tempDocURI(t testing.TB, name string) uri.URI {
+	t.Helper()
+	return uri.File(filepath.Join(t.TempDir(), name))
+}
+
+// testDocURI is the URI a helper opens name under: an absolute name as given,
+// a bare one in a directory of the test's own.
+func testDocURI(t testing.TB, name string) uri.URI {
+	t.Helper()
+	if filepath.IsAbs(name) {
+		u := uri.File(name)
+		requireTestOwnedDir(t, u)
+		return u
+	}
+	return tempDocURI(t, name)
+}
+
+// requireTestOwnedDir fails a test about to open u in a directory it does not
+// own: the working directory, where a bare name lands, or the system temp directory.
+func requireTestOwnedDir(t testing.TB, u uri.URI) {
+	t.Helper()
+	dir := filepath.Dir(u.Filename())
+	wd, err := os.Getwd()
+	if err != nil {
+		t.Fatalf("Getwd: %v", err)
+	}
+	if dir == wd || dir == os.TempDir() {
+		t.Fatalf("document %s opens in shared directory %s; use tempDocURI", u, dir)
+	}
+}
diff --git a/tests/hygiene/size_test.go b/tests/hygiene/size_test.go
index f046f46be2..e03be7a372 100644
--- a/tests/hygiene/size_test.go
+++ b/tests/hygiene/size_test.go
@@ -35,7 +35,7 @@ var oversizeTestFiles = []oversize{
 	{"internal/exec/runtime/conformance_test.go", 2714, "execution-conformance driver and its per-case assertions"},
 	{"internal/exec/runtime/signal_test.go", 2491, "signal delivery scenarios on one shared harness"},
 	{"tests/migrate/behavior_more_test.go", 2465, "SysML v1 behavior migration scenarios on one shared harness"},
-	{"internal/frontend/lsp/debug_test.go", 2203, "LSP debug-protocol scenarios over one wire fixture"},
+	{"internal/frontend/lsp/debug_test.go", 2127, "LSP debug-protocol scenarios over one wire fixture"},
 	{"internal/exec/runtime/signal_injection_test.go", 2181, "signal-injection scenarios on one shared harness"},
 	{"internal/exec/runtime/adopt_test.go", 2163, "adoption scenarios on one shared harness"},
 	{"internal/doc/queryexec/execute_test.go", 2114, "query-execution scenarios on one shared harness"},