diff --git a/.chronus/changes/fix-java-emitter-build-progress-hang-2026-07-21-17-30-00.md b/.chronus/changes/fix-java-emitter-build-progress-hang-2026-07-21-17-30-00.md
new file mode 100644
index 0000000000..01b5d90b28
--- /dev/null
+++ b/.chronus/changes/fix-java-emitter-build-progress-hang-2026-07-21-17-30-00.md
@@ -0,0 +1,7 @@
+---
+changeKind: internal
+packages:
+  - "@azure-tools/typespec-java"
+---
+
+Fix the Java emitter build intermittently hanging a full parallel `pnpm build`. The build scripts run under turbo, which puts each task in a background process group under the build's controlling terminal; when a PowerShell cmdlet (notably `Copy-Item -Recurse`) rendered `Write-Progress`, pwsh touched that terminal and the OS stopped it with SIGTTIN/SIGTTOU, hanging forever. The `.ps1` build scripts now set `$ProgressPreference = 'SilentlyContinue'`. Also make the pinned-`core/` fetch conditional (only when the commit is missing) and non-interactive (`GIT_TERMINAL_PROMPT=0`, `pwsh -NonInteractive`) to remove secondary hang/network vectors.
diff --git a/packages/typespec-java/Build-Generator.ps1 b/packages/typespec-java/Build-Generator.ps1
index 437b78acf5..2e75a5b461 100644
--- a/packages/typespec-java/Build-Generator.ps1
+++ b/packages/typespec-java/Build-Generator.ps1
@@ -10,6 +10,11 @@
 
 $ErrorActionPreference = "Stop"
 
+# See Copy-Sources.ps1: silence progress so no cmdlet touches the controlling
+# terminal from turbo's background process group (which would SIGTTIN/SIGTTOU-stop
+# this process and hang the parallel build).
+$ProgressPreference = "SilentlyContinue"
+
 $packageRoot = $PSScriptRoot
 $generatorRoot = Join-Path $packageRoot "generator"
 $generatorPom = Join-Path $generatorRoot "pom.xml"
diff --git a/packages/typespec-java/Copy-Sources.ps1 b/packages/typespec-java/Copy-Sources.ps1
index 607b8db41a..45c8e6f8e1 100644
--- a/packages/typespec-java/Copy-Sources.ps1
+++ b/packages/typespec-java/Copy-Sources.ps1
@@ -13,6 +13,16 @@
 
 $ErrorActionPreference = "Stop"
 
+# Disable progress rendering. Under a full parallel `pnpm build`, turbo runs each
+# task's process in its own background process group under the build's controlling
+# terminal. When a cmdlet here (notably `Copy-Item -Recurse`, which emits a
+# Write-Progress) renders progress, PowerShell touches that terminal from a
+# background process group and the OS stops the process with SIGTTIN/SIGTTOU -- it
+# never resumes, so the emitter build appears to hang forever (intermittently, and
+# only for this package since it is the only one that shells out to pwsh). Silencing
+# progress removes that terminal interaction entirely.
+$ProgressPreference = "SilentlyContinue"
+
 $packageRoot = $PSScriptRoot
 $repoRoot = Resolve-Path (Join-Path $packageRoot ".." "..")
 $coreRoot = Join-Path $repoRoot "core"
diff --git a/packages/typespec-java/CoreCommit.ps1 b/packages/typespec-java/CoreCommit.ps1
index 3cbc8299fb..815dcbe29e 100644
--- a/packages/typespec-java/CoreCommit.ps1
+++ b/packages/typespec-java/CoreCommit.ps1
@@ -41,6 +41,19 @@ function Get-CoreSourceRoot {
         [string] $PackageRoot
     )
 
+    # Never let any git invocation below block on an interactive credential or
+    # host-key prompt. During a parallel `pnpm build` the emitter build runs
+    # headless (turbo captures its stdio / attaches a pseudo-terminal), so a git
+    # prompt has nowhere to read from and would hang the whole build forever --
+    # observed as an intermittent, Java-only build hang. Make git fail fast instead.
+    $env:GIT_TERMINAL_PROMPT = "0"
+
+    # Silence progress: a cmdlet rendering Write-Progress (e.g. the archive
+    # extraction below) touches the controlling terminal, and under turbo's
+    # background process group that stops this process with SIGTTIN/SIGTTOU and
+    # hangs the build. Scoped to this function so callers are unaffected.
+    $ProgressPreference = "SilentlyContinue"
+
     $originSha = (git -C $CoreRoot rev-parse HEAD).Trim()
     if ($LASTEXITCODE -ne 0) {
         Write-Error "Failed to read the current SHA of the 'core' submodule at: $CoreRoot`nMake sure it is checked out (git submodule update --init --recursive)."
@@ -65,9 +78,17 @@ function Get-CoreSourceRoot {
         return @{ Root = $liveRoot; TempDir = $null }
     }
 
-    # Make sure the target commit is available locally (it may be newer than what
-    # has been fetched); ignore failure if it is already present.
-    git -C $CoreRoot fetch --quiet origin $targetSha 2>$null
+    # Make sure the target commit is available locally (the pin may be newer than
+    # what has been fetched). Only hit the network when the commit is genuinely
+    # missing: this code runs on EVERY emitter build and doc regen, and a `git
+    # fetch` on core/ is the only per-build network operation in the whole repo
+    # build, so doing it unconditionally turns any transient network/credential
+    # stall into a Java-only build hang. `git cat-file -e <sha>^{commit}` is a
+    # cheap, offline existence check.
+    git -C $CoreRoot cat-file -e "${targetSha}^{commit}" 2>$null
+    if ($LASTEXITCODE -ne 0) {
+        git -C $CoreRoot fetch --quiet origin $targetSha 2>$null
+    }
 
     # Only move forward: use the target when it is a descendant (newer) of the
     # current checkout. `merge-base --is-ancestor A B` exits 0 when A is an ancestor
@@ -85,23 +106,31 @@ function Get-CoreSourceRoot {
     $tempDir = Join-Path ([System.IO.Path]::GetTempPath()) ("typespec-java-core-" + [System.Guid]::NewGuid().ToString("N"))
     New-Item -ItemType Directory -Path $tempDir | Out-Null
     $zipPath = Join-Path $tempDir "core.zip"
+    $extractDir = Join-Path $tempDir "src"
     try {
-        # Produce a zip (not tar) and expand it with the built-in Expand-Archive:
+        # Produce a zip (not tar) and expand it with .NET's ZipFile.ExtractToDirectory:
         # this keeps the whole flow inside PowerShell/.NET and avoids depending on an
         # external `tar`, whose behavior varies by platform (notably Git for Windows'
         # GNU tar treats a drive-letter path like C:\...\core.tar as a remote host).
+        #
+        # ExtractToDirectory is used instead of Expand-Archive on purpose: the archived
+        # subtree holds several thousand files, and Expand-Archive emits a per-entry
+        # Write-Progress that makes it pathologically slow on that many files (worse when
+        # its output is captured by a parallel `pnpm build`), to the point the emitter
+        # build looks hung. ZipFile.ExtractToDirectory has no such overhead.
         git -C $CoreRoot archive --format=zip -o $zipPath "${targetSha}:$script:CoreJavaSubtree"
         if ($LASTEXITCODE -ne 0) {
             Write-Error "Failed to archive core commit ${targetSha}:$script:CoreJavaSubtree."
         }
-        Expand-Archive -Path $zipPath -DestinationPath $tempDir -Force
+        Add-Type -AssemblyName System.IO.Compression.FileSystem
+        [System.IO.Compression.ZipFile]::ExtractToDirectory($zipPath, $extractDir)
     }
     catch {
         Remove-Item $tempDir -Recurse -Force -ErrorAction SilentlyContinue
         throw
     }
     Remove-Item $zipPath -Force
-    return @{ Root = $tempDir; TempDir = $tempDir }
+    return @{ Root = $extractDir; TempDir = $tempDir }
 }
 
 # Clean up the temporary extraction created by Get-CoreSourceRoot (no-op when the
diff --git a/packages/typespec-java/package.json b/packages/typespec-java/package.json
index b8aa438970..43e339844e 100644
--- a/packages/typespec-java/package.json
+++ b/packages/typespec-java/package.json
@@ -30,8 +30,8 @@
   "scripts": {
     "clean": "rimraf ./dist ./temp ./generator",
     "build": "pnpm build:emitter && pnpm build:generator",
-    "build:emitter": "pwsh -NoProfile -File Copy-Sources.ps1 && tsc -p .",
-    "build:generator": "pwsh -NoProfile -File Build-Generator.ps1",
+    "build:emitter": "pwsh -NoProfile -NonInteractive -File Copy-Sources.ps1 && tsc -p .",
+    "build:generator": "pwsh -NoProfile -NonInteractive -File Build-Generator.ps1",
     "watch": "tsc -p . --watch",
     "test": "vitest run",
     "regen-docs": "pnpm run build:emitter && tspd doc . --enable-experimental --output-dir ../../website/src/content/docs/docs/emitters/clients/typespec-java/reference --skip-js"