[ANE-2795] Fix UTF-8 encoding for ficus output on Windows (#1646)

* Fix UTF-8 encoding crash when reading ficus stderr on Windows

Use Conduit with decodeUtf8Lenient for stderr handling, matching the
approach already used for stdout. This prevents crashes on Windows
where the default system encoding (CP1252) cannot decode UTF-8 characters
like box-drawing characters (U+2501) used in ficus progress output.

The decodeUtf8Lenient function safely handles any byte sequence by
replacing invalid UTF-8 with the Unicode replacement character (U+FFFD)
instead of throwing an exception.

Fixes: ANE-2795

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Co-Authored-By: Claude <noreply@anthropic.com>

* Fix UTF-8 encoding when writing ficus debug logs on Windows

Set explicit UTF-8 encoding on debug log file handles. On Windows,
file handles default to the system code page (CP1252), which cannot
encode Unicode characters like box-drawing characters (U+2501) used
in ficus's Rust SPANTRACE output.

Without this fix, running `fossa analyze --x-vendetta --debug` on
Windows crashes with:
  commitBuffer: invalid argument (cannot encode character '\9473')

This complements the previous fix for reading ficus output by ensuring
the writing side also handles UTF-8 correctly.

Fixes: ANE-2795

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

* Simplify stderr accumulator and fix formatting

- Remove redundant count tracking from stderr fold (take 50 on a bounded
  list is already O(1))
- Use Text throughout msg construction instead of String intermediates
- Remove trailing blank line to satisfy formatter

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: Conor-FOSSA

Changelog.md

@@ -1,5 +1,9 @@
 # FOSSA CLI Changelog
 
+## Unreleased
+
+- Windows: Fix UTF-8 encoding crash when running `fossa analyze --x-vendetta --debug` on native Windows. The CLI no longer crashes when subprocess output contains Unicode characters. ([#1646](https://github.com/fossas/fossa-cli/pull/1646))
+
 ## 3.16.5
 
 - PNPM: Fix pnpm v9 lockfile transitive devDependency classification. Dependencies of devDependencies were incorrectly reported as production dependencies in pnpm v9 projects. ([#1668](https://github.com/fossas/fossa-cli/pull/1668))

src/App/Fossa/Ficus/Analyze.hs

@@ -58,7 +58,7 @@ import Path (Abs, Dir, Path, toFilePath)
 import Prettyprinter (pretty)
 import Srclib.Types (Locator (..), SourceUnit (..), SourceUnitBuild (..), SourceUnitDependency (..), renderLocator, textToOriginPath)
 import System.FilePath ((</>))
-import System.IO (Handle, IOMode (WriteMode), hClose, hGetLine, hIsEOF, hPutStrLn, openFile, stderr)
+import System.IO (Handle, IOMode (WriteMode), hClose, hPutStrLn, hSetEncoding, openFile, stderr, utf8)
 import System.Process.Typed (
   createPipe,
   getStderr,
@@ -265,7 +265,9 @@ runFicus maybeDebugDir ficusConfig = do
           let stdoutPath = debugDir </> "fossa.ficus-stdout.log"
           let stderrPath = debugDir </> "fossa.ficus-stderr.log"
           stdoutH <- openFile stdoutPath WriteMode
+          hSetEncoding stdoutH utf8
           stderrH <- openFile stderrPath WriteMode
+          hSetEncoding stderrH utf8
           pure (Just stdoutH, Just stderrH)
       Nothing ->
         -- No debug mode, don't tee to files
@@ -354,32 +356,29 @@ runFicus maybeDebugDir ficusConfig = do
           , vendoredDependencyScanResults = vendoredResults
           }
 
+    -- Use Conduit with decodeUtf8Lenient to safely handle UTF-8 output from ficus.
+    -- This matches the approach used for stdout and prevents crashes on Windows
+    -- where the default system encoding (CP1252) cannot decode UTF-8 characters
+    -- like box-drawing characters (U+2501) used in ficus progress output.
     consumeStderr :: Handle -> Maybe Handle -> IO [Text]
     consumeStderr handle maybeFile = do
-      let loop acc (count :: Int) = do
-            eof <- hIsEOF handle
-            if eof
-              then pure (reverse acc) -- Reverse at the end to get correct order
-              else do
-                line <- hGetLine handle
-                -- Tee raw line to file if debug mode
-                traverse_ (`hPutStrLn` line) maybeFile
-                now <- getCurrentTime
-                let timestamp = formatTime defaultTimeLocale "%H:%M:%S.%3q" now
-                let msg = "[" ++ timestamp ++ "] STDERR " <> line
-                -- Keep at most the last 50 lines of stderr
-                -- I came up with 50 lines by looking at a few different error traces and making
-                -- sure that we captured all of the relevant error output, and then going a bit higher
-                -- to make sure that we didn't miss anything. I'd rather capture a bit too much than not enough.
-                -- Use cons (:) for O(1) prepending, track count explicitly for O(1) truncation
-                let newAcc =
-                      if count >= 50
-                        then take 50 (toText msg : acc)
-                        else toText msg : acc
-                let newCount = min (count + 1) 50
-                loop newAcc newCount
-      loop [] 0
-
+      acc <-
+        Conduit.runConduit $
+          CC.sourceHandle handle
+            .| CC.decodeUtf8Lenient
+            .| CC.linesUnbounded
+            .| CC.foldM
+              ( \acc line -> do
+                  -- Tee raw line to file if debug mode
+                  traverse_ (\fileH -> hPutStrLn fileH (toString line)) maybeFile
+                  now <- getCurrentTime
+                  -- Keep at most the last 50 lines of stderr (newest first during accumulation)
+                  let ts = toText $ formatTime defaultTimeLocale "%H:%M:%S.%3q" now
+                  let msg = "[" <> ts <> "] STDERR " <> line
+                  pure (take 50 (msg : acc))
+              )
+              []
+      pure (reverse acc)
     displayFicusDebug :: FicusDebug -> Text
     displayFicusDebug (FicusDebug FicusMessageData{..}) = ficusMessageDataStrategy <> ": " <> ficusMessageDataPayload
     displayFicusError :: FicusError -> Text