diff --git a/crates/native-sidecar/src/execution.rs b/crates/native-sidecar/src/execution.rs
index a23d0cff08..6448bb7583 100644
--- a/crates/native-sidecar/src/execution.rs
+++ b/crates/native-sidecar/src/execution.rs
@@ -41,7 +41,8 @@ use crate::state::{
     JavascriptTlsDataValue, JavascriptTlsMaterial, JavascriptUdpFamily, JavascriptUdpSocketEvent,
     JavascriptUnixListenerEvent, KernelSocketReadinessEvent, KernelSocketReadinessRegistry,
     KernelSocketReadinessTarget, LoopbackTlsPendingWriteHandle, LoopbackTlsPendingWriteState,
-    NetworkResourceCounts, PendingTcpSocket, PendingUnixSocket, ProcNetEntry, ProcessEventEnvelope,
+    NetworkResourceCounts, PendingKernelStdin, PendingTcpSocket, PendingUnixSocket, ProcNetEntry,
+    ProcessEventEnvelope,
     PythonHostSocket, ResolvedChildProcessExecution, ResolvedTcpConnectAddr, SharedBridge,
     SharedSidecarRequestClient, SidecarKernel, SocketQueryKind, ToolExecution, VmDnsConfig,
     VmListenPolicy, VmState, DEFAULT_JAVASCRIPT_NET_BACKLOG, EXECUTION_DRIVER_NAME,
@@ -471,6 +472,7 @@ impl ActiveProcess {
             kernel_pid,
             kernel_handle,
             kernel_stdin_writer_fd: None,
+            pending_kernel_stdin: PendingKernelStdin::default(),
             tty_master_fd: None,
             runtime,
             detached: false,
@@ -7885,6 +7887,11 @@ where
         {
             return Ok(false);
         }
+        // Top off the child's stdin pipe from any host-side backlog before
+        // probing readiness: the child draining the pipe is exactly what frees
+        // capacity for the next queued stdin bytes (and, once the backlog is
+        // empty, executes a deferred stdin close so EOF arrives in order).
+        flush_pending_kernel_stdin(kernel, child)?;
         let now = Instant::now();
         let requested_timeout_ms = match request.method.as_str() {
             "__kernel_stdin_read" => parse_kernel_stdin_read_args(request)?.1,
@@ -19509,6 +19516,20 @@ fn install_kernel_stdin_pipe(kernel: &mut SidecarKernel, pid: u32) -> Result<u32
             agentos_kernel::fd_table::FD_CLOEXEC,
         )
         .map_err(kernel_error)?;
+    // Non-blocking writes only: the sidecar dispatch thread feeds this pipe
+    // from `write_kernel_process_stdin` / `flush_pending_kernel_stdin`, and a
+    // blocking pipe write would deadlock — the child's pipe reads are parked
+    // sync RPCs serviced by this same thread. A full pipe surfaces EAGAIN and
+    // the remainder is queued in `ActiveProcess::pending_kernel_stdin`.
+    kernel
+        .fd_fcntl(
+            EXECUTION_DRIVER_NAME,
+            pid,
+            write_fd,
+            agentos_kernel::fd_table::F_SETFL,
+            agentos_kernel::fd_table::O_NONBLOCK,
+        )
+        .map_err(kernel_error)?;
     Ok(write_fd)
 }
 
@@ -19533,6 +19554,13 @@ fn javascript_child_process_stdin_mode(request: &JavascriptChildProcessSpawnRequ
         .unwrap_or("pipe")
 }
 
+/// Host-side cap on stdin bytes queued for a child's kernel pipe. Matches the
+/// kernel's default per-write bound (`resource.max_fd_write_bytes`); a parent
+/// cannot park more than this behind a slow child before getting a typed
+/// error.
+const MAX_PENDING_KERNEL_STDIN_BYTES: usize =
+    agentos_kernel::resource_accounting::DEFAULT_MAX_FD_WRITE_BYTES;
+
 pub(crate) fn write_kernel_process_stdin(
     kernel: &mut SidecarKernel,
     process: &mut ActiveProcess,
@@ -19548,17 +19576,103 @@ pub(crate) fn write_kernel_process_stdin(
     let Some(writer_fd) = process.kernel_stdin_writer_fd else {
         return Ok(());
     };
-    kernel
-        .fd_write(EXECUTION_DRIVER_NAME, process.kernel_pid, writer_fd, chunk)
-        .map_err(kernel_error)?;
-    // For a TTY process the master write above drives line-discipline echo into
-    // the master output buffer. Drain it now and surface it as the single
-    // ordered Stdout stream so typed-character echo reaches the host even while
-    // the guest is blocked in read() and not producing output of its own.
-    if let Some(echo) = drain_tty_master_output(kernel, process)? {
-        process.queue_pending_execution_event(ActiveExecutionEvent::Stdout(echo))?;
-    }
-    forward_tty_slave_input_to_javascript(kernel, process)?;
+    if process.tty_master_fd.is_some() {
+        kernel
+            .fd_write(EXECUTION_DRIVER_NAME, process.kernel_pid, writer_fd, chunk)
+            .map_err(kernel_error)?;
+        // For a TTY process the master write above drives line-discipline echo
+        // into the master output buffer. Drain it now and surface it as the
+        // single ordered Stdout stream so typed-character echo reaches the
+        // host even while the guest is blocked in read() and not producing
+        // output of its own.
+        if let Some(echo) = drain_tty_master_output(kernel, process)? {
+            process.queue_pending_execution_event(ActiveExecutionEvent::Stdout(echo))?;
+        }
+        forward_tty_slave_input_to_javascript(kernel, process)?;
+        return Ok(());
+    }
+    // Pipe-backed stdin. The kernel pipe caps at MAX_PIPE_BUFFER_BYTES and
+    // fd_write reports POSIX partial writes, so anything the pipe cannot take
+    // right now is queued and flushed as the child drains (see
+    // `flush_pending_kernel_stdin`). Silently dropping the remainder is how
+    // multi-buffer stdin payloads (e.g. git's spooled pack piped into
+    // `index-pack --stdin`) used to truncate at 64 KiB.
+    let pending_total = process.pending_kernel_stdin.total;
+    if pending_total.saturating_add(chunk.len()) > MAX_PENDING_KERNEL_STDIN_BYTES {
+        return Err(SidecarError::InvalidState(format!(
+            "child process stdin backlog limit exceeded: {pending_total} pending + {} new bytes \
+             > {MAX_PENDING_KERNEL_STDIN_BYTES} (MAX_PENDING_KERNEL_STDIN_BYTES); the child is \
+             not draining stdin — write smaller chunks after the child consumes them, or raise \
+             this bound together with the kernel resource.max_fd_write_bytes limit",
+            chunk.len(),
+        )));
+    }
+    process.pending_kernel_stdin.push(chunk);
+    flush_pending_kernel_stdin(kernel, process)
+}
+
+/// Write as much queued stdin as the child's kernel pipe can take right now.
+/// Called on every stdin write and from the child kernel-wait servicing path
+/// (each parked `__kernel_stdin_read` / `__kernel_poll` re-check), so the
+/// backlog drains in lockstep with the child's reads. Executes the deferred
+/// stdin close once the backlog is empty.
+pub(crate) fn flush_pending_kernel_stdin(
+    kernel: &mut SidecarKernel,
+    process: &mut ActiveProcess,
+) -> Result<(), SidecarError> {
+    if process.tty_master_fd.is_some() {
+        return Ok(());
+    }
+    let Some(writer_fd) = process.kernel_stdin_writer_fd else {
+        process.pending_kernel_stdin.clear();
+        process.pending_kernel_stdin.close_requested = false;
+        return Ok(());
+    };
+    while let Some(front) = process.pending_kernel_stdin.chunks.pop_front() {
+        let offset = process.pending_kernel_stdin.front_offset;
+        let slice = &front[offset..];
+        match kernel.fd_write(EXECUTION_DRIVER_NAME, process.kernel_pid, writer_fd, slice) {
+            Ok(written) if written >= slice.len() => {
+                process.pending_kernel_stdin.total =
+                    process.pending_kernel_stdin.total.saturating_sub(slice.len());
+                process.pending_kernel_stdin.front_offset = 0;
+            }
+            Ok(written) => {
+                // Pipe is full mid-chunk; keep the remainder queued.
+                process.pending_kernel_stdin.total =
+                    process.pending_kernel_stdin.total.saturating_sub(written);
+                process.pending_kernel_stdin.front_offset = offset + written;
+                process.pending_kernel_stdin.chunks.push_front(front);
+                break;
+            }
+            Err(error) if error.code() == "EAGAIN" => {
+                process.pending_kernel_stdin.chunks.push_front(front);
+                break;
+            }
+            Err(error) if error.code() == "EPIPE" => {
+                // Reader side is gone (child exited or closed stdin): drop the
+                // backlog and release the writer, mirroring a SIGPIPE'd POSIX
+                // writer.
+                process.pending_kernel_stdin.clear();
+                process.pending_kernel_stdin.close_requested = false;
+                process.kernel_stdin_writer_fd = None;
+                let _ = kernel.fd_close(EXECUTION_DRIVER_NAME, process.kernel_pid, writer_fd);
+                return Ok(());
+            }
+            Err(error) => {
+                process.pending_kernel_stdin.chunks.push_front(front);
+                return Err(kernel_error(error));
+            }
+        }
+    }
+    if process.pending_kernel_stdin.is_empty() && process.pending_kernel_stdin.close_requested {
+        process.pending_kernel_stdin.close_requested = false;
+        if let Some(writer_fd) = process.kernel_stdin_writer_fd.take() {
+            kernel
+                .fd_close(EXECUTION_DRIVER_NAME, process.kernel_pid, writer_fd)
+                .map_err(kernel_error)?;
+        }
+    }
     Ok(())
 }
 
@@ -19605,6 +19719,13 @@ pub(crate) fn close_kernel_process_stdin(
     kernel: &mut SidecarKernel,
     process: &mut ActiveProcess,
 ) -> Result<(), SidecarError> {
+    if !process.pending_kernel_stdin.is_empty() && process.kernel_stdin_writer_fd.is_some() {
+        // Queued stdin has not reached the pipe yet; closing now would hand
+        // the child a premature EOF. `flush_pending_kernel_stdin` performs the
+        // close once the backlog drains.
+        process.pending_kernel_stdin.close_requested = true;
+        return Ok(());
+    }
     let Some(writer_fd) = process.kernel_stdin_writer_fd.take() else {
         return Ok(());
     };
diff --git a/crates/native-sidecar/src/state.rs b/crates/native-sidecar/src/state.rs
index 3004ec7b36..973d8534df 100644
--- a/crates/native-sidecar/src/state.rs
+++ b/crates/native-sidecar/src/state.rs
@@ -449,11 +449,49 @@ impl Default for VmListenPolicy {
 // Active process state
 // ---------------------------------------------------------------------------
 
+/// Stdin bytes accepted from a parent's `child_process.write_stdin` but not
+/// yet written into the child's kernel stdin pipe. The kernel pipe holds at
+/// most `MAX_PIPE_BUFFER_BYTES` (64 KiB) and `fd_write` reports partial
+/// writes with POSIX pipe semantics, so multi-buffer stdin payloads (for
+/// example git's spooled pack fed to `index-pack --stdin`) must be queued
+/// host-side and flushed as the child drains its pipe. `close_requested`
+/// defers the writer-fd close until the backlog fully drains so the child
+/// never observes an early EOF.
+#[derive(Default)]
+pub(crate) struct PendingKernelStdin {
+    pub(crate) chunks: VecDeque<Vec<u8>>,
+    /// Bytes of the front chunk already written into the pipe.
+    pub(crate) front_offset: usize,
+    /// Total unwritten bytes across all queued chunks.
+    pub(crate) total: usize,
+    pub(crate) close_requested: bool,
+}
+
+impl PendingKernelStdin {
+    pub(crate) fn is_empty(&self) -> bool {
+        self.chunks.is_empty()
+    }
+
+    pub(crate) fn push(&mut self, chunk: &[u8]) {
+        self.total += chunk.len();
+        self.chunks.push_back(chunk.to_vec());
+    }
+
+    pub(crate) fn clear(&mut self) {
+        self.chunks.clear();
+        self.front_offset = 0;
+        self.total = 0;
+    }
+}
+
 #[allow(dead_code)]
 pub(crate) struct ActiveProcess {
     pub(crate) kernel_pid: u32,
     pub(crate) kernel_handle: KernelProcessHandle,
     pub(crate) kernel_stdin_writer_fd: Option<u32>,
+    /// Backlog for pipe-backed kernel stdin awaiting pipe capacity; see
+    /// [`PendingKernelStdin`].
+    pub(crate) pending_kernel_stdin: PendingKernelStdin,
     /// For a TTY (PTY-backed) process, the master-end fd whose output buffer
     /// carries cooked-mode echo plus ONLCR-processed guest output. When set,
     /// this master output is the single ordered output stream surfaced to the
diff --git a/crates/native-sidecar/tests/fixtures/limits-inventory.json b/crates/native-sidecar/tests/fixtures/limits-inventory.json
index 65f5098b8a..08e26cf1a1 100644
--- a/crates/native-sidecar/tests/fixtures/limits-inventory.json
+++ b/crates/native-sidecar/tests/fixtures/limits-inventory.json
@@ -1114,5 +1114,11 @@
 		"path": "crates/execution/src/wasm.rs",
 		"class": "invariant",
 		"rationale": "Host-side LRU entry cap for cached wasm module bytes; process-wide cache sizing, not per-VM policy."
+	},
+	{
+		"name": "MAX_PENDING_KERNEL_STDIN_BYTES",
+		"path": "crates/native-sidecar/src/execution.rs",
+		"class": "policy-deferred",
+		"rationale": "Host-side backlog cap for child stdin awaiting kernel pipe capacity; mirrors resource.max_fd_write_bytes, not yet wired to VmLimits."
 	}
 ]
diff --git a/packages/runtime-core/commands/git b/packages/runtime-core/commands/git
index f2dc7a774c..0a577332dc 100644
Binary files a/packages/runtime-core/commands/git and b/packages/runtime-core/commands/git differ
diff --git a/packages/runtime-core/commands/git-receive-pack b/packages/runtime-core/commands/git-receive-pack
index f2dc7a774c..0a577332dc 100644
Binary files a/packages/runtime-core/commands/git-receive-pack and b/packages/runtime-core/commands/git-receive-pack differ
diff --git a/packages/runtime-core/commands/git-remote-http b/packages/runtime-core/commands/git-remote-http
index 124c54b4e9..8c78d028ca 100644
Binary files a/packages/runtime-core/commands/git-remote-http and b/packages/runtime-core/commands/git-remote-http differ
diff --git a/packages/runtime-core/commands/git-remote-https b/packages/runtime-core/commands/git-remote-https
index 124c54b4e9..8c78d028ca 100644
Binary files a/packages/runtime-core/commands/git-remote-https and b/packages/runtime-core/commands/git-remote-https differ
diff --git a/packages/runtime-core/commands/git-upload-archive b/packages/runtime-core/commands/git-upload-archive
index f2dc7a774c..0a577332dc 100644
Binary files a/packages/runtime-core/commands/git-upload-archive and b/packages/runtime-core/commands/git-upload-archive differ
diff --git a/packages/runtime-core/commands/git-upload-pack b/packages/runtime-core/commands/git-upload-pack
index f2dc7a774c..0a577332dc 100644
Binary files a/packages/runtime-core/commands/git-upload-pack and b/packages/runtime-core/commands/git-upload-pack differ
diff --git a/toolchain/c/scripts/build-git-upstream.sh b/toolchain/c/scripts/build-git-upstream.sh
index 304e004647..40d343a530 100755
--- a/toolchain/c/scripts/build-git-upstream.sh
+++ b/toolchain/c/scripts/build-git-upstream.sh
@@ -121,6 +121,15 @@ CURL_CFLAGS="-I$CURL_PREFIX/include"
 CURL_LDFLAGS="-L$CURL_PREFIX/lib -lcurl -L$MBEDTLS_LIBDIR -lmbedtls -lmbedx509 -lmbedcrypto -L$ZLIB_BUILD_DIR -lz -L$BROTLI_LIBDIR -lbrotlidec -lbrotlicommon -L$ZSTD_LIBDIR -lzstd"
 
 echo "Building upstream Git ${VERSION} for wasm32-wasip1 (with in-process libcurl)..."
+# Stack layout: wasm-ld defaults to a 64 KiB stack placed *above* the data
+# segment. Git assumes native-sized stacks (recv_sideband alone puts a
+# LARGE_PACKET_MAX (~64 KiB) buffer on the stack, reached several frames deep
+# on every sideband pack transfer), so with the default layout the buffer
+# silently overwrites static data and clones/fetches die with wild wasm traps
+# once packs carry payloads bigger than a few KiB. Give git an 8 MiB stack
+# (glibc-default sized) and --stack-first so any future overflow traps at the
+# faulting frame instead of corrupting the data segment.
+GIT_WASM_STACK_FLAGS="-Wl,-z,stack-size=8388608 -Wl,--stack-first"
 make -j"${MAKE_JOBS:-2}" \
   uname_S=WASI \
   CC="$CC_CMD" \
@@ -128,7 +137,7 @@ make -j"${MAKE_JOBS:-2}" \
   AR="$AR_CMD" \
   RANLIB="$RANLIB_CMD" \
   CFLAGS="--target=wasm32-wasip1 --sysroot=$SYSROOT -I$ZLIB_DIR -O2 -D_WASI_EMULATED_PROCESS_CLOCKS -D_WASI_EMULATED_MMAN" \
-  LDFLAGS="--target=wasm32-wasip1 --sysroot=$SYSROOT -L$ZLIB_BUILD_DIR -lwasi-emulated-process-clocks -lwasi-emulated-mman" \
+  LDFLAGS="--target=wasm32-wasip1 --sysroot=$SYSROOT -L$ZLIB_BUILD_DIR -lwasi-emulated-process-clocks -lwasi-emulated-mman $GIT_WASM_STACK_FLAGS" \
   CURL_CFLAGS="$CURL_CFLAGS" \
   CURL_LDFLAGS="$CURL_LDFLAGS" \
   CSPRNG_METHOD=getentropy \
diff --git a/toolchain/c/sysroot/lib/wasm32-wasi/libc.a b/toolchain/c/sysroot/lib/wasm32-wasi/libc.a
index aa37ca6c17..f253c97663 100644
Binary files a/toolchain/c/sysroot/lib/wasm32-wasi/libc.a and b/toolchain/c/sysroot/lib/wasm32-wasi/libc.a differ