Fix segfault: add mutex for ANSI terminal operations

Problem: Intermittent segfaults when running `bild --time 0 **/*` with
many concurrent builds. Core dumps showed crashes in libncursesw's
free() function during terminal cleanup.

Root cause: ANSI.getTerminalSize and other ANSI terminal library
calls are not thread-safe. With mapConcurrentlyBounded running up to
8 analyses concurrently, multiple threads were calling ANSI functions
simultaneously, causing memory corruption in the ncurses library.

Solution: Add global MVar terminalLock to serialize all ANSI terminal
operations. Wrap all ANSI function calls (cursor movement, line
clearing, etc.) with withMVar terminalLock.

Changes: - Add terminalLock :: MVar () in Omni/Log/Concurrent.hs -
Wrap all ANSI calls in withMVar terminalLock:
  - initializeLines: cursor column, clear line - updateLine: cursor
  up/down, column set, clear line - updateLineState: cursor up/down,
  column set, clear line - withLineManager: cursor up

Tested: 5 consecutive runs of `bild --time 0 **/*` complete without
segfaults (previously failed 1-2 out of 3 runs).

1 files changed, 51 insertions, 42 deletions

diff --git a/Omni/Log/Concurrent.hs b/Omni/Log/Concurrent.hs
index edf87fd..b43c8ef 100644
--- a/Omni/Log/Concurrent.hs
+++ b/Omni/Log/Concurrent.hs
@@ -42,6 +42,12 @@ currentLineManager = unsafePerformIO (newIORef Nothing)
 namespaceLines :: IORef (Map Namespace Int)
 namespaceLines = unsafePerformIO (newIORef Map.empty)
 
+-- | Global lock for all terminal operations
+-- ANSI terminal library is not thread-safe, so we must serialize all calls
+{-# NOINLINE terminalLock #-}
+terminalLock :: MVar ()
+terminalLock = unsafePerformIO (newMVar ())
+
 withLineManager :: [Namespace] -> (LineManager -> IO a) -> IO a
 withLineManager nss action = do
   termInfo <- detectTerminal
@@ -61,7 +67,7 @@ withLineManager nss action = do
       let numLines = min (length nss) (tiHeight termInfo - 2)
       IO.hPutStrLn IO.stderr ""
       replicateM_ numLines (IO.hPutStrLn IO.stderr "")
-      ANSI.hCursorUp IO.stderr numLines
+      withMVar terminalLock <| \_ -> ANSI.hCursorUp IO.stderr numLines
 
       let mgr = LineManager {lmNamespaces = nss, lmTermInfo = termInfo}
       writeIORef currentLineManager (Just mgr)
@@ -84,14 +90,15 @@ initializeLines LineManager {..} =
     (SingleLine, _) -> pure () -- No initialization needed
     (MultiLine, _) -> do
       nsMap <- readIORef namespaceLines
-      forM_ (Map.toList nsMap) <| \(ns, _) -> do
-        ANSI.hSetCursorColumn IO.stderr 0
-        ANSI.hClearLine IO.stderr
-        let nsText = Text.pack (Namespace.toPath ns)
-        let msg = "[+] " <> nsText
-        let truncated = truncateToWidth (tiWidth lmTermInfo - 1) msg
-        IO.hPutStrLn IO.stderr (Text.unpack truncated)
-        IO.hFlush IO.stderr
+      forM_ (Map.toList nsMap) <| \(ns, _) ->
+        withMVar terminalLock <| \_ -> do
+          ANSI.hSetCursorColumn IO.stderr 0
+          ANSI.hClearLine IO.stderr
+          let nsText = Text.pack (Namespace.toPath ns)
+          let msg = "[+] " <> nsText
+          let truncated = truncateToWidth (tiWidth lmTermInfo - 1) msg
+          IO.hPutStrLn IO.stderr (Text.unpack truncated)
+          IO.hFlush IO.stderr
 
 updateLine :: Namespace -> Text -> IO ()
 updateLine ns output = do
@@ -124,22 +131,23 @@ updateLine ns output = do
           nsMap <- readIORef namespaceLines
           case Map.lookup ns nsMap of
             Nothing -> pure ()
-            Just lineNum -> do
-              let numLines = length lmNamespaces
-              -- Move to the target line from bottom
-              ANSI.hCursorUp IO.stderr (numLines - lineNum)
-              ANSI.hSetCursorColumn IO.stderr 0
-              ANSI.hClearLine IO.stderr
-              let nsText = Text.pack (Namespace.toPath ns)
-              let msg =
-                    if Text.null output
-                      then "[~] " <> nsText
-                      else "[~] " <> nsText <> ": " <> output
-              let truncated = truncateToWidth (tiWidth lmTermInfo - 1) msg
-              IO.hPutStr IO.stderr (Text.unpack truncated)
-              IO.hFlush IO.stderr
-              -- Move back to bottom
-              ANSI.hCursorDown IO.stderr (numLines - lineNum)
+            Just lineNum ->
+              withMVar terminalLock <| \_ -> do
+                let numLines = length lmNamespaces
+                -- Move to the target line from bottom
+                ANSI.hCursorUp IO.stderr (numLines - lineNum)
+                ANSI.hSetCursorColumn IO.stderr 0
+                ANSI.hClearLine IO.stderr
+                let nsText = Text.pack (Namespace.toPath ns)
+                let msg =
+                      if Text.null output
+                        then "[~] " <> nsText
+                        else "[~] " <> nsText <> ": " <> output
+                let truncated = truncateToWidth (tiWidth lmTermInfo - 1) msg
+                IO.hPutStr IO.stderr (Text.unpack truncated)
+                IO.hFlush IO.stderr
+                -- Move back to bottom
+                ANSI.hCursorDown IO.stderr (numLines - lineNum)
 
 updateLineState :: Namespace -> BuildState -> IO ()
 updateLineState ns buildState = do
@@ -170,20 +178,21 @@ updateLineState ns buildState = do
           nsMap <- readIORef namespaceLines
           case Map.lookup ns nsMap of
             Nothing -> pure ()
-            Just lineNum -> do
-              let numLines = length lmNamespaces
-              ANSI.hCursorUp IO.stderr (numLines - lineNum)
-              ANSI.hSetCursorColumn IO.stderr 0
-              ANSI.hClearLine IO.stderr
-              let nsText = Text.pack (Namespace.toPath ns)
-              let (symbol, colorFn) = case buildState of
-                    Success -> ("✓", fore green)
-                    Failed -> ("x", fore red)
-                    Analyzing -> ("+", identity)
-                    Pending -> ("…", identity)
-                    Building -> ("~", identity)
-              let msg = "[" <> symbol <> "] " <> nsText
-              let truncated = truncateToWidth (tiWidth lmTermInfo - 1) msg
-              Rainbow.hPutChunks IO.stderr [colorFn <| chunk truncated]
-              IO.hFlush IO.stderr
-              ANSI.hCursorDown IO.stderr (numLines - lineNum)
+            Just lineNum ->
+              withMVar terminalLock <| \_ -> do
+                let numLines = length lmNamespaces
+                ANSI.hCursorUp IO.stderr (numLines - lineNum)
+                ANSI.hSetCursorColumn IO.stderr 0
+                ANSI.hClearLine IO.stderr
+                let nsText = Text.pack (Namespace.toPath ns)
+                let (symbol, colorFn) = case buildState of
+                      Success -> ("✓", fore green)
+                      Failed -> ("x", fore red)
+                      Analyzing -> ("+", identity)
+                      Pending -> ("…", identity)
+                      Building -> ("~", identity)
+                let msg = "[" <> symbol <> "] " <> nsText
+                let truncated = truncateToWidth (tiWidth lmTermInfo - 1) msg
+                Rainbow.hPutChunks IO.stderr [colorFn <| chunk truncated]
+                IO.hFlush IO.stderr
+                ANSI.hCursorDown IO.stderr (numLines - lineNum)