3 files changed, 132 insertions, 31 deletions
diff --git a/packages/app/src/components/titlebar-history.test.ts b/packages/app/src/components/titlebar-history.test.ts
new file mode 100644
index 000000000..25035d7cc
--- /dev/null
+++ b/packages/app/src/components/titlebar-history.test.ts
@@ -0,0 +1,63 @@
+import { describe, expect, test } from "bun:test"
+import { applyPath, backPath, forwardPath, type TitlebarHistory } from "./titlebar-history"
+
+function history(): TitlebarHistory {
+  return { stack: [], index: 0, action: undefined }
+}
+
+describe("titlebar history", () => {
+  test("append and trim keeps max bounded", () => {
+    let state = history()
+    state = applyPath(state, "/", 3)
+    state = applyPath(state, "/a", 3)
+    state = applyPath(state, "/b", 3)
+    state = applyPath(state, "/c", 3)
+
+    expect(state.stack).toEqual(["/a", "/b", "/c"])
+    expect(state.stack.length).toBe(3)
+    expect(state.index).toBe(2)
+  })
+
+  test("back and forward indexes stay correct after trimming", () => {
+    let state = history()
+    state = applyPath(state, "/", 3)
+    state = applyPath(state, "/a", 3)
+    state = applyPath(state, "/b", 3)
+    state = applyPath(state, "/c", 3)
+
+    expect(state.stack).toEqual(["/a", "/b", "/c"])
+    expect(state.index).toBe(2)
+
+    const back = backPath(state)
+    expect(back?.to).toBe("/b")
+    expect(back?.state.index).toBe(1)
+
+    const afterBack = applyPath(back!.state, back!.to, 3)
+    expect(afterBack.stack).toEqual(["/a", "/b", "/c"])
+    expect(afterBack.index).toBe(1)
+
+    const forward = forwardPath(afterBack)
+    expect(forward?.to).toBe("/c")
+    expect(forward?.state.index).toBe(2)
+
+    const afterForward = applyPath(forward!.state, forward!.to, 3)
+    expect(afterForward.stack).toEqual(["/a", "/b", "/c"])
+    expect(afterForward.index).toBe(2)
+  })
+
+  test("action-driven navigation does not push duplicate history entries", () => {
+    const state: TitlebarHistory = {
+      stack: ["/", "/a", "/b"],
+      index: 2,
+      action: undefined,
+    }
+
+    const back = backPath(state)
+    expect(back?.to).toBe("/a")
+
+    const next = applyPath(back!.state, back!.to, 10)
+    expect(next.stack).toEqual(["/", "/a", "/b"])
+    expect(next.index).toBe(1)
+    expect(next.action).toBeUndefined()
+  })
+})
diff --git a/packages/app/src/components/titlebar-history.ts b/packages/app/src/components/titlebar-history.ts
new file mode 100644
index 000000000..44dbbfa3a
--- /dev/null
+++ b/packages/app/src/components/titlebar-history.ts
@@ -0,0 +1,57 @@
+export const MAX_TITLEBAR_HISTORY = 100
+
+export type TitlebarAction = "back" | "forward" | undefined
+
+export type TitlebarHistory = {
+  stack: string[]
+  index: number
+  action: TitlebarAction
+}
+
+export function applyPath(state: TitlebarHistory, current: string, max = MAX_TITLEBAR_HISTORY): TitlebarHistory {
+  if (!state.stack.length) {
+    const stack = current === "/" ? ["/"] : ["/", current]
+    return { stack, index: stack.length - 1, action: undefined }
+  }
+
+  const active = state.stack[state.index]
+  if (current === active) {
+    if (!state.action) return state
+    return { ...state, action: undefined }
+  }
+
+  if (state.action) return { ...state, action: undefined }
+
+  return pushPath(state, current, max)
+}
+
+export function pushPath(state: TitlebarHistory, path: string, max = MAX_TITLEBAR_HISTORY): TitlebarHistory {
+  const stack = state.stack.slice(0, state.index + 1).concat(path)
+  const next = trimHistory(stack, stack.length - 1, max)
+  return { ...state, ...next, action: undefined }
+}
+
+export function trimHistory(stack: string[], index: number, max = MAX_TITLEBAR_HISTORY) {
+  if (stack.length <= max) return { stack, index }
+  const cut = stack.length - max
+  return {
+    stack: stack.slice(cut),
+    index: Math.max(0, index - cut),
+  }
+}
+
+export function backPath(state: TitlebarHistory) {
+  if (state.index <= 0) return
+  const index = state.index - 1
+  const to = state.stack[index]
+  if (!to) return
+  return { state: { ...state, index, action: "back" as const }, to }
+}
+
+export function forwardPath(state: TitlebarHistory) {
+  if (state.index >= state.stack.length - 1) return
+  const index = state.index + 1
+  const to = state.stack[index]
+  if (!to) return
+  return { state: { ...state, index, action: "forward" as const }, to }
+}
diff --git a/packages/app/src/components/titlebar.tsx b/packages/app/src/components/titlebar.tsx
index 32e36815e..d8735410a 100644
--- a/packages/app/src/components/titlebar.tsx
+++ b/packages/app/src/components/titlebar.tsx
@@ -11,6 +11,7 @@ import { useLayout } from "@/context/layout"
 import { usePlatform } from "@/context/platform"
 import { useCommand } from "@/context/command"
 import { useLanguage } from "@/context/language"
+import { applyPath, backPath, forwardPath } from "./titlebar-history"
 
 export function Titlebar() {
   const layout = useLayout()
@@ -39,25 +40,9 @@ export function Titlebar() {
     const current = path()
 
     untrack(() => {
-      if (!history.stack.length) {
-        const stack = current === "/" ? ["/"] : ["/", current]
-        setHistory({ stack, index: stack.length - 1 })
-        return
-      }
-
-      const active = history.stack[history.index]
-      if (current === active) {
-        if (history.action) setHistory("action", undefined)
-        return
-      }
-
-      if (history.action) {
-        setHistory("action", undefined)
-        return
-      }
-
-      const next = history.stack.slice(0, history.index + 1).concat(current)
-      setHistory({ stack: next, index: next.length - 1 })
+      const next = applyPath(history, current)
+      if (next === history) return
+      setHistory(next)
     })
   })
 
@@ -65,21 +50,17 @@ export function Titlebar() {
   const canForward = createMemo(() => history.index < history.stack.length - 1)
 
   const back = () => {
-    if (!canBack()) return
-    const index = history.index - 1
-    const to = history.stack[index]
-    if (!to) return
-    setHistory({ index, action: "back" })
-    navigate(to)
+    const next = backPath(history)
+    if (!next) return
+    setHistory(next.state)
+    navigate(next.to)
   }
 
   const forward = () => {
-    if (!canForward()) return
-    const index = history.index + 1
-    const to = history.stack[index]
-    if (!to) return
-    setHistory({ index, action: "forward" })
-    navigate(to)
+    const next = forwardPath(history)
+    if (!next) return
+    setHistory(next.state)
+    navigate(next.to)
   }
 
   command.register(() => [