Add server-side and test-side port retry mechanisms to handle race conditions

- Introduced a new plan to address port-in-use race conditions in both server and test environments.
- Implemented a retry mechanism with exponential backoff for binding to known ports in `LiveServer::start()`.
- Added a `respawn_with_new_port()` method in `TestServeSession` to handle transient port conflicts during tests.
- Modified `wait_to_come_online()` to retry with a new port if the server process exits due to `AddrInUse`.
- Updated `fresh_rebuild_read()` to include port retry logic, enhancing robustness against port conflicts.

These changes aim to improve the reliability of server and test interactions by mitigating race conditions related to port usage.

.cursor/plans/fix_test_port_toctou_86726cb4.plan.md

@@ -0,0 +1,104 @@
+---
+name: Fix test port TOCTOU
+overview: Two-layer fix for port-in-use race conditions. (1) Server-side -- retry bind with backoff when a known port is busy. (2) Test-side -- retry with a new random port when the serve process dies from AddrInUse.
+todos:
+  - id: server-bind-retry
+    content: Add bind retry with backoff in `LiveServer::start()` for known ports
+    status: completed
+  - id: respawn-method
+    content: Add `respawn_with_new_port()` method to `TestServeSession`
+    status: completed
+  - id: wait-retry
+    content: Modify `wait_to_come_online()` to detect AddrInUse and retry via respawn
+    status: completed
+  - id: fresh-rebuild-retry
+    content: Add port-retry logic to `fresh_rebuild_read()`
+    status: completed
+isProject: false
+---
+
+# Fix Port-in-Use Race Conditions
+
+## Problem
+
+Two failure modes:
+
+1. **Tests (random ports):** `get_port_number()` in `[tests/rojo_test/serve_util.rs](tests/rojo_test/serve_util.rs)` binds port 0, reads the assigned port, drops the listener, then passes the port to the spawned serve process. Another test can grab the same port in that TOCTOU window.
+2. **Server (known ports):** `TcpListener::bind(address).await.unwrap()` in `[src/web/mod.rs:80](src/web/mod.rs)` panics immediately if the port is in use, with no retry. A previous server instance shutting down or a transient conflict gives no grace period.
+
+## Layer 1: Server-side bind retry (`src/web/mod.rs`)
+
+Replace the `.unwrap()` on `TcpListener::bind()` at line 80 with a retry loop:
+
+- On `AddrInUse`: retry up to 5 times with exponential backoff (200ms, 400ms, 800ms, 1600ms, 3200ms -- ~6s total)
+- On any other bind error, or after retries exhausted: return `anyhow::Error` (propagates up cleanly instead of panicking)
+
+```rust
+let listener = {
+    const MAX_BIND_RETRIES: u32 = 5;
+    const BASE_BACKOFF_MS: u64 = 200;
+    let mut last_err = None;
+    for attempt in 0..MAX_BIND_RETRIES {
+        match TcpListener::bind(address).await {
+            Ok(listener) => { last_err = None; break; }
+            Err(err) if err.kind() == std::io::ErrorKind::AddrInUse => {
+                let delay = BASE_BACKOFF_MS * 2u64.pow(attempt);
+                log::warn!(
+                    "Port {} in use, retrying in {}ms (attempt {}/{})",
+                    address.port(), delay, attempt + 1, MAX_BIND_RETRIES
+                );
+                tokio::time::sleep(Duration::from_millis(delay)).await;
+                last_err = Some(err);
+            }
+            Err(err) => { last_err = Some(err); break; }
+        }
+    }
+    // unwrap or propagate
+};
+```
+
+This helps both tests (brief TOCTOU window) and production (previous process releasing a port).
+
+## Layer 2: Test-side retry with new random port (`tests/rojo_test/serve_util.rs`)
+
+If the serve process still dies after the server-side retries (e.g., the port is held long-term by another test), the test infrastructure retries with a completely new port.
+
+### 2a. Add `respawn_with_new_port()` to `TestServeSession`
+
+Kills the current process, picks a new ephemeral port, and respawns:
+
+```rust
+fn respawn_with_new_port(&mut self) {
+    let port = get_port_number();
+    let port_string = port.to_string();
+    let working_dir = get_working_dir_path();
+
+    let rojo_process = Command::new(ROJO_PATH)
+        .args(["serve", self.project_path.to_str().unwrap(), "--port", &port_string])
+        .current_dir(working_dir)
+        .stderr(Stdio::piped())
+        .spawn()
+        .expect("Couldn't start Rojo");
+
+    self.rojo_process = KillOnDrop(rojo_process);
+    self.port = port;
+}
+```
+
+### 2b. Modify `wait_to_come_online()`
+
+In the `Ok(Some(status))` branch (line ~266-276), detect `AddrInUse` in stderr and retry:
+
+- Add a `port_retries` counter (max 3 attempts)
+- On `AddrInUse`: call `self.respawn_with_new_port()`, reset the backoff counter, continue
+- On other errors: panic as before
+
+### 2c. Apply same pattern to `fresh_rebuild_read()`
+
+`fresh_rebuild_read()` (line ~929) has its own inline wait loop. Wrap the spawn + wait in a retry loop that detects `AddrInUse` and retries with a new port.
+
+## Files changed
+
+- `[src/web/mod.rs](src/web/mod.rs)` -- bind retry with backoff (Layer 1)
+- `[tests/rojo_test/serve_util.rs](tests/rojo_test/serve_util.rs)` -- respawn with new port (Layer 2)
+

plugin/src/App/Components/TableDiffVisualizer/Dictionary.lua

@@ -7,6 +7,7 @@ local Roact = require(Packages.Roact)
 local Timer = require(Plugin.Timer)
 local Assets = require(Plugin.Assets)
 local Theme = require(Plugin.App.Theme)
+local trueEquals = require(Plugin.Reconciler.trueEquals)
 
 local ScrollingFrame = require(Plugin.App.Components.ScrollingFrame)
 local DisplayValue = require(Plugin.App.Components.PatchVisualizer.DisplayValue)
@@ -35,8 +36,7 @@ function Dictionary:calculateDiff()
 				key = key,
 				patchType = "Remove",
 			})
-		elseif newValue ~= oldValue then
-			-- Note: should this do some sort of deep comparison for various types?
+		elseif not trueEquals(oldValue, newValue) then
 			table.insert(diff, {
 				key = key,
 				patchType = "Edit",

plugin/src/Reconciler/trueEquals.lua

@@ -157,8 +157,11 @@ local function trueEquals(a: any, b: any): boolean
 		end
 		return true
 	end
+	if t == "Font" then
+		return a.Family == b.Family and a.Weight == b.Weight and a.Style == b.Style
+	end
 
-	return false
+	return a == b
 end
 
 return trueEquals

plugin/src/Reconciler/trueEquals.spec.lua

@@ -593,6 +593,265 @@ return function()
 		end)
 	end)
 
+	describe("Font", function()
+		it("identical fonts", function()
+			local a =
+				Font.new("rbxasset://fonts/families/SourceSansPro.json", Enum.FontWeight.Regular, Enum.FontStyle.Normal)
+			local b =
+				Font.new("rbxasset://fonts/families/SourceSansPro.json", Enum.FontWeight.Regular, Enum.FontStyle.Normal)
+			expect(trueEquals(a, b)).to.equal(true)
+		end)
+
+		it("different family", function()
+			local a =
+				Font.new("rbxasset://fonts/families/SourceSansPro.json", Enum.FontWeight.Regular, Enum.FontStyle.Normal)
+			local b =
+				Font.new("rbxasset://fonts/families/RobotoMono.json", Enum.FontWeight.Regular, Enum.FontStyle.Normal)
+			expect(trueEquals(a, b)).to.equal(false)
+		end)
+
+		it("different weight", function()
+			local a =
+				Font.new("rbxasset://fonts/families/SourceSansPro.json", Enum.FontWeight.Regular, Enum.FontStyle.Normal)
+			local b =
+				Font.new("rbxasset://fonts/families/SourceSansPro.json", Enum.FontWeight.Bold, Enum.FontStyle.Normal)
+			expect(trueEquals(a, b)).to.equal(false)
+		end)
+
+		it("different style", function()
+			local a =
+				Font.new("rbxasset://fonts/families/SourceSansPro.json", Enum.FontWeight.Regular, Enum.FontStyle.Normal)
+			local b =
+				Font.new("rbxasset://fonts/families/SourceSansPro.json", Enum.FontWeight.Regular, Enum.FontStyle.Italic)
+			expect(trueEquals(a, b)).to.equal(false)
+		end)
+
+		it("same reference via rawequal", function()
+			local a = Font.new("rbxasset://fonts/families/SourceSansPro.json")
+			expect(trueEquals(a, a)).to.equal(true)
+		end)
+
+		it("semibold vs regular", function()
+			local a = Font.new(
+				"rbxasset://fonts/families/SourceSansPro.json",
+				Enum.FontWeight.SemiBold,
+				Enum.FontStyle.Normal
+			)
+			local b =
+				Font.new("rbxasset://fonts/families/SourceSansPro.json", Enum.FontWeight.Regular, Enum.FontStyle.Normal)
+			expect(trueEquals(a, b)).to.equal(false)
+		end)
+	end)
+
+	describe("BrickColor", function()
+		it("same BrickColor", function()
+			expect(trueEquals(BrickColor.new("Bright red"), BrickColor.new("Bright red"))).to.equal(true)
+		end)
+
+		it("different BrickColor", function()
+			expect(trueEquals(BrickColor.new("Bright red"), BrickColor.new("Bright blue"))).to.equal(false)
+		end)
+	end)
+
+	describe("fallback == equality", function()
+		it("true vs true", function()
+			expect(trueEquals(true, true)).to.equal(true)
+		end)
+
+		it("false vs false", function()
+			expect(trueEquals(false, false)).to.equal(true)
+		end)
+
+		it("true vs false", function()
+			expect(trueEquals(true, false)).to.equal(false)
+		end)
+
+		it("false vs true", function()
+			expect(trueEquals(false, true)).to.equal(false)
+		end)
+
+		it("same string content", function()
+			expect(trueEquals("hello", "hello")).to.equal(true)
+		end)
+
+		it("different string content", function()
+			expect(trueEquals("hello", "world")).to.equal(false)
+		end)
+
+		it("empty strings", function()
+			expect(trueEquals("", "")).to.equal(true)
+		end)
+
+		it("same Axes", function()
+			expect(trueEquals(Axes.new(Enum.Axis.X, Enum.Axis.Y), Axes.new(Enum.Axis.X, Enum.Axis.Y))).to.equal(true)
+		end)
+
+		it("different Axes", function()
+			expect(trueEquals(Axes.new(Enum.Axis.X), Axes.new(Enum.Axis.Y))).to.equal(false)
+		end)
+
+		it("same Faces", function()
+			expect(trueEquals(Faces.new(Enum.NormalId.Top), Faces.new(Enum.NormalId.Top))).to.equal(true)
+		end)
+
+		it("different Faces", function()
+			expect(trueEquals(Faces.new(Enum.NormalId.Top), Faces.new(Enum.NormalId.Bottom))).to.equal(false)
+		end)
+
+		it("same Region3int16", function()
+			local a = Region3int16.new(Vector3int16.new(0, 0, 0), Vector3int16.new(10, 10, 10))
+			local b = Region3int16.new(Vector3int16.new(0, 0, 0), Vector3int16.new(10, 10, 10))
+			expect(trueEquals(a, b)).to.equal(true)
+		end)
+
+		it("different Region3int16", function()
+			local a = Region3int16.new(Vector3int16.new(0, 0, 0), Vector3int16.new(10, 10, 10))
+			local b = Region3int16.new(Vector3int16.new(0, 0, 0), Vector3int16.new(20, 20, 20))
+			expect(trueEquals(a, b)).to.equal(false)
+		end)
+
+		it("same Vector3int16", function()
+			expect(trueEquals(Vector3int16.new(1, 2, 3), Vector3int16.new(1, 2, 3))).to.equal(true)
+		end)
+
+		it("different Vector3int16", function()
+			expect(trueEquals(Vector3int16.new(1, 2, 3), Vector3int16.new(4, 5, 6))).to.equal(false)
+		end)
+
+		it("same Vector2int16", function()
+			expect(trueEquals(Vector2int16.new(1, 2), Vector2int16.new(1, 2))).to.equal(true)
+		end)
+
+		it("different Vector2int16", function()
+			expect(trueEquals(Vector2int16.new(1, 2), Vector2int16.new(3, 4))).to.equal(false)
+		end)
+
+		it("same PhysicalProperties", function()
+			local a = PhysicalProperties.new(1, 0.5, 0.3)
+			local b = PhysicalProperties.new(1, 0.5, 0.3)
+			expect(trueEquals(a, b)).to.equal(true)
+		end)
+
+		it("different PhysicalProperties", function()
+			local a = PhysicalProperties.new(1, 0.5, 0.3)
+			local b = PhysicalProperties.new(2, 0.5, 0.3)
+			expect(trueEquals(a, b)).to.equal(false)
+		end)
+
+		it("different Instances are not equal", function()
+			local a = Instance.new("Folder")
+			local b = Instance.new("Folder")
+			expect(trueEquals(a, b)).to.equal(false)
+			a:Destroy()
+			b:Destroy()
+		end)
+
+		it("same EnumItem via fallback", function()
+			expect(trueEquals(Enum.SortOrder.LayoutOrder, Enum.SortOrder.LayoutOrder)).to.equal(true)
+		end)
+
+		it("different EnumItems of same enum", function()
+			expect(trueEquals(Enum.SortOrder.LayoutOrder, Enum.SortOrder.Name)).to.equal(false)
+		end)
+	end)
+
+	describe("attribute dictionaries", function()
+		it("identical Color3 attributes", function()
+			local a = { BackgroundColor = Color3.fromRGB(32, 34, 39), TextSize = 14 }
+			local b = { BackgroundColor = Color3.fromRGB(32, 34, 39), TextSize = 14 }
+			expect(trueEquals(a, b)).to.equal(true)
+		end)
+
+		it("Color3 cleanup_f32 precision", function()
+			local a = Color3.fromRGB(32, 34, 39)
+			local b = Color3.new(0.125490, 0.133333, 0.152941)
+			expect(trueEquals(a, b)).to.equal(true)
+		end)
+
+		it("dict with Color3 cleanup_f32 precision", function()
+			local a = { BackgroundColor = Color3.fromRGB(32, 34, 39) }
+			local b = { BackgroundColor = Color3.new(0.125490, 0.133333, 0.152941) }
+			expect(trueEquals(a, b)).to.equal(true)
+		end)
+
+		it("dict with Font values", function()
+			local font = Font.new(
+				"rbxasset://fonts/families/SourceSansPro.json",
+				Enum.FontWeight.SemiBold,
+				Enum.FontStyle.Normal
+			)
+			local a = { LabelFont = font }
+			local b = {
+				LabelFont = Font.new(
+					"rbxasset://fonts/families/SourceSansPro.json",
+					Enum.FontWeight.SemiBold,
+					Enum.FontStyle.Normal
+				),
+			}
+			expect(trueEquals(a, b)).to.equal(true)
+		end)
+
+		it("dict with mixed types matching", function()
+			local a = {
+				BackgroundColor = Color3.fromRGB(128, 128, 128),
+				Transparency = 0.25,
+				Size = 14,
+				Label = "Hello",
+				LabelFont = Font.new(
+					"rbxasset://fonts/families/SourceSansPro.json",
+					Enum.FontWeight.Regular,
+					Enum.FontStyle.Normal
+				),
+				Corner = UDim.new(0, 8),
+			}
+			local b = {
+				BackgroundColor = Color3.fromRGB(128, 128, 128),
+				Transparency = 0.25,
+				Size = 14,
+				Label = "Hello",
+				LabelFont = Font.new(
+					"rbxasset://fonts/families/SourceSansPro.json",
+					Enum.FontWeight.Regular,
+					Enum.FontStyle.Normal
+				),
+				Corner = UDim.new(0, 8),
+			}
+			expect(trueEquals(a, b)).to.equal(true)
+		end)
+
+		it("dict with one Font mismatch fails whole table", function()
+			local a = {
+				BackgroundColor = Color3.fromRGB(128, 128, 128),
+				LabelFont = Font.new(
+					"rbxasset://fonts/families/SourceSansPro.json",
+					Enum.FontWeight.Regular,
+					Enum.FontStyle.Normal
+				),
+			}
+			local b = {
+				BackgroundColor = Color3.fromRGB(128, 128, 128),
+				LabelFont = Font.new(
+					"rbxasset://fonts/families/SourceSansPro.json",
+					Enum.FontWeight.Bold,
+					Enum.FontStyle.Normal
+				),
+			}
+			expect(trueEquals(a, b)).to.equal(false)
+		end)
+
+		it("extra key in new table", function()
+			local a = { BackgroundColor = Color3.new(1, 0, 0) }
+			local b = { BackgroundColor = Color3.new(1, 0, 0), NewAttr = "hello" }
+			expect(trueEquals(a, b)).to.equal(false)
+		end)
+
+		it("missing key in new table", function()
+			local a = { BackgroundColor = Color3.new(1, 0, 0), OldAttr = "hello" }
+			local b = { BackgroundColor = Color3.new(1, 0, 0) }
+			expect(trueEquals(a, b)).to.equal(false)
+		end)
+	end)
+
 	describe("type mismatches", function()
 		it("string vs number", function()
 			expect(trueEquals("hello", 42)).to.equal(false)

src/web/mod.rs

@@ -11,6 +11,7 @@ mod util;
 use std::convert::Infallible;
 use std::net::SocketAddr;
 use std::sync::{Arc, Mutex};
+use std::time::Duration;
 
 use hyper::body::Incoming;
 use hyper::server::conn::http1;
@@ -77,7 +78,37 @@ impl LiveServer {
 
         let rt = Runtime::new().unwrap();
         let exit_reason = rt.block_on(async move {
-            let listener = TcpListener::bind(address).await.unwrap();
+            let listener = {
+                const MAX_BIND_ATTEMPTS: u32 = 5;
+                const BASE_BACKOFF_MS: u64 = 200;
+                let mut attempts = 0u32;
+                loop {
+                    attempts += 1;
+                    match TcpListener::bind(address).await {
+                        Ok(listener) => break listener,
+                        Err(err)
+                            if err.kind() == std::io::ErrorKind::AddrInUse
+                                && attempts < MAX_BIND_ATTEMPTS =>
+                        {
+                            let delay = BASE_BACKOFF_MS * 2u64.pow(attempts - 1);
+                            log::warn!(
+                                "Port {} in use, retrying in {}ms (attempt {}/{})",
+                                address.port(),
+                                delay,
+                                attempts,
+                                MAX_BIND_ATTEMPTS
+                            );
+                            tokio::time::sleep(Duration::from_millis(delay)).await;
+                        }
+                        Err(err) => {
+                            panic!(
+                                "Failed to bind to {}: {} (after {} attempts)",
+                                address, err, attempts
+                            );
+                        }
+                    }
+                }
+            };
 
             loop {
                 tokio::select! {

tests/rojo_test/serve_util.rs

@@ -256,13 +256,39 @@ impl TestServeSession {
         self.port
     }
 
-    /// Waits for the `rojo serve` server to come online with expontential
-    /// backoff.
+    fn respawn_with_new_port(&mut self) {
+        let port = get_port_number();
+        let port_string = port.to_string();
+        let working_dir = get_working_dir_path();
+
+        let rojo_process = Command::new(ROJO_PATH)
+            .args([
+                "serve",
+                self.project_path.to_str().unwrap(),
+                "--port",
+                port_string.as_str(),
+            ])
+            .current_dir(working_dir)
+            .stderr(Stdio::piped())
+            .spawn()
+            .expect("Couldn't start Rojo");
+
+        self.rojo_process = KillOnDrop(rojo_process);
+        self.port = port;
+    }
+
+    /// Waits for the `rojo serve` server to come online with exponential
+    /// backoff. If the process dies with `AddrInUse`, respawns with a new
+    /// random port (up to `MAX_PORT_RETRIES` times).
     pub fn wait_to_come_online(&mut self) -> ServerInfoResponse {
         const BASE_DURATION_MS: f32 = 30.0;
         const EXP_BACKOFF_FACTOR: f32 = 1.3;
         const MAX_TRIES: u32 = 5;
+        const MAX_PORT_RETRIES: u32 = 3;
 
+        let mut port_retries = 0u32;
+
+        'retry_port: loop {
             for i in 1..=MAX_TRIES {
                 match self.rojo_process.0.try_wait() {
                     Ok(Some(status)) => {
@@ -270,6 +296,17 @@ impl TestServeSession {
                         if let Some(mut stderr) = self.rojo_process.0.stderr.take() {
                             let _ = stderr.read_to_string(&mut stderr_output);
                         }
+                        if stderr_output.contains("AddrInUse") && port_retries < MAX_PORT_RETRIES {
+                            port_retries += 1;
+                            log::warn!(
+                                "Port {} in use, respawning with new port (attempt {}/{})",
+                                self.port,
+                                port_retries,
+                                MAX_PORT_RETRIES
+                            );
+                            self.respawn_with_new_port();
+                            continue 'retry_port;
+                        }
                         panic!(
                             "Rojo process exited with status {}\nstderr:\n{}",
                             status, stderr_output
@@ -298,6 +335,7 @@ impl TestServeSession {
 
             panic!("Rojo server did not respond after {} tries.", MAX_TRIES);
         }
+    }
 
     pub fn get_api_rojo(&self) -> Result<ServerInfoResponse, reqwest::Error> {
         let url = format!("http://localhost:{}/api/rojo", self.port);
@@ -938,9 +976,17 @@ pub fn fresh_rebuild_read(project_path: &Path) -> NormalizedInstance {
         );
     };
 
+    const BASE_DURATION_MS: f32 = 30.0;
+    const EXP_BACKOFF_FACTOR: f32 = 1.3;
+    const MAX_TRIES: u32 = 5;
+    const MAX_PORT_RETRIES: u32 = 3;
+
+    let working_dir = get_working_dir_path();
+    let mut port_retries = 0u32;
+
+    loop {
         let port = get_port_number();
         let port_string = port.to_string();
-    let working_dir = get_working_dir_path();
 
         let process = Command::new(ROJO_PATH)
             .args([
@@ -949,19 +995,15 @@ pub fn fresh_rebuild_read(project_path: &Path) -> NormalizedInstance {
                 "--port",
                 port_string.as_str(),
             ])
-        .current_dir(working_dir)
+            .current_dir(&working_dir)
             .stderr(Stdio::piped())
             .spawn()
             .expect("Couldn't start fresh Rojo for round-trip check");
 
         let mut kill_guard = KillOnDrop(process);
-
-    // Wait for fresh server to come online with same backoff
-    const BASE_DURATION_MS: f32 = 30.0;
-    const EXP_BACKOFF_FACTOR: f32 = 1.3;
-    const MAX_TRIES: u32 = 5;
-
         let mut info = None;
+        let mut needs_port_retry = false;
+
         for i in 1..=MAX_TRIES {
             match kill_guard.0.try_wait() {
                 Ok(Some(status)) => {
@@ -969,6 +1011,17 @@ pub fn fresh_rebuild_read(project_path: &Path) -> NormalizedInstance {
                     if let Some(mut stderr) = kill_guard.0.stderr.take() {
                         let _ = stderr.read_to_string(&mut stderr_output);
                     }
+                    if stderr_output.contains("AddrInUse") && port_retries < MAX_PORT_RETRIES {
+                        port_retries += 1;
+                        log::warn!(
+                            "Port {} in use, retrying with new port (attempt {}/{})",
+                            port,
+                            port_retries,
+                            MAX_PORT_RETRIES
+                        );
+                        needs_port_retry = true;
+                        break;
+                    }
                     panic!(
                         "Fresh Rojo process exited with status {}\nstderr:\n{}",
                         status, stderr_output
@@ -991,6 +1044,10 @@ pub fn fresh_rebuild_read(project_path: &Path) -> NormalizedInstance {
             thread::sleep(Duration::from_millis(retry_time_ms as u64));
         }
 
+        if needs_port_retry {
+            continue;
+        }
+
         let info = info.expect("Fresh Rojo server did not respond");
         let root_id = info.root_instance_id;
 
@@ -1002,7 +1059,8 @@ pub fn fresh_rebuild_read(project_path: &Path) -> NormalizedInstance {
         let read: ReadResponse =
             deserialize_msgpack(&body).expect("Fresh server returned malformed response");
 
-    normalize_read_response(&read, root_id)
+        return normalize_read_response(&read, root_id);
+    }
 }
 
 /// Assert that the live session tree matches a fresh rebuild from the filesystem.