diff --git a/MODULE.bazel b/MODULE.bazel
index 1d21ea2f79..90161b23f2 100644
--- a/MODULE.bazel
+++ b/MODULE.bazel
@@ -83,6 +83,20 @@ register_toolchains(
     dev_dependency = True,
 )
 
+# sv-lang (via tools/OpenROAD) pulls in rules_pycross, whose toolchain
+# extension fails on Python 3.8 (transitively registered via or-tools ->
+# pybind11_abseil, dropped from rules_python 2.0.0's MINOR_MAPPING).
+# pycross.configure_environments is root-honored only, so the workaround
+# must be mirrored here from tools/OpenROAD/MODULE.bazel.
+bazel_dep(name = "rules_pycross", version = "0.8.1", dev_dependency = True)
+
+pycross = use_extension(
+    "@rules_pycross//pycross/extensions:pycross.bzl",
+    "pycross",
+    dev_dependency = True,
+)
+pycross.configure_environments(python_versions = ["3.13"])
+
 python = use_extension("@rules_python//python/extensions:python.bzl", "python")
 python.toolchain(
     ignore_root_user_error = True,
diff --git a/flow/designs/asap7/gcd/BUILD b/flow/designs/asap7/gcd/BUILD
index 527d6542e1..9674a4de33 100644
--- a/flow/designs/asap7/gcd/BUILD
+++ b/flow/designs/asap7/gcd/BUILD
@@ -1,3 +1,143 @@
+load("@bazel-orfs//:openroad.bzl", "orfs_run")
+load("@orfs_designs//:designs.bzl", "DESIGNS")
+load("@rules_shell//shell:sh_test.bzl", "sh_test")
 load("//flow/designs:design.bzl", "design")
 
-design(config = "config.mk")
+# SYNTH_USE_SYN is make-only for now: bazel-orfs's synth stage always
+# runs the yosys flow and neither stages the Verilog sources nor sets
+# VERILOG_FILES for the OpenROAD synthesis step, so the built-in
+# synthesizer opt-in must not reach the bazel arguments.
+design(
+    config = "config.mk",
+    local_arguments = ["SYNTH_USE_SYN"],
+)
+
+# Stage-boundary .odb/.sdc stems shared by the normal per-stage flow
+# targets and the single-process flow below; gcd_single_flow_test
+# compares each of these files pairwise between the two flows.
+SINGLE_FLOW_STAGES = {
+    "floorplan": "2_floorplan",
+    "place": "3_place",
+    "cts": "4_cts",
+    "grt": "5_1_grt",
+    "route": "5_route",
+    "final": "6_final",
+}
+
+# Substep files the single-process flow also writes, declared so the
+# action keeps them and a human can inspect them on failure.
+SINGLE_FLOW_EXTRA_OUTS = [
+    "2_1_floorplan.odb",
+    "2_1_floorplan.sdc",
+    "2_2_floorplan_macro.odb",
+    "2_3_floorplan_tapcell.odb",
+    "2_4_floorplan_pdn.odb",
+    "3_1_place_gp_skip_io.odb",
+    "3_2_place_iop.odb",
+    "3_3_place_gp.odb",
+    "3_4_place_resized.odb",
+    "3_5_place_dp.odb",
+    "4_1_cts.odb",
+    "5_2_route.odb",
+    "5_3_fillcell.odb",
+    "6_1_fill.odb",
+    "6_1_fill.sdc",
+]
+
+# The whole flow, floorplan through finish, as one Tcl script in a
+# single OpenROAD process (scripts/flow.tcl). The synth stage config
+# only carries synth-scoped variables, so the design's full argument
+# set rides along; FLOW_VARIANT=single keeps the output paths clear of
+# the regular stage targets' declared outputs in this package.
+orfs_run(
+    name = "gcd_single_flow",
+    src = ":gcd_synth",
+    outs = [
+        "results/asap7/gcd/single/{}.{}".format(stem, ext)
+        for stem in SINGLE_FLOW_STAGES.values()
+        for ext in [
+            "odb",
+            "sdc",
+        ]
+    ] + [
+        "results/asap7/gcd/single/" + name
+        for name in SINGLE_FLOW_EXTRA_OUTS
+    ],
+    arguments = {
+        k: v
+        for k, v in DESIGNS["asap7/gcd"]["arguments"].items()
+        if k != "SYNTH_USE_SYN"
+    } | {
+        "FLOW_VARIANT": "single",
+    },
+    script = ":single_flow.tcl",
+    variant = "single",
+)
+
+# Normal-flow stage outputs, one filegroup per compared file.
+[
+    filegroup(
+        name = "gcd_base_{}_{}".format(stage, ext),
+        srcs = [":gcd_" + stage],
+        output_group = "{}.{}".format(stem, ext),
+    )
+    for stage, stem in SINGLE_FLOW_STAGES.items()
+    for ext in [
+        "odb",
+        "sdc",
+    ]
+]
+
+# Byte-compare each stage boundary's .odb/.sdc between the per-stage
+# flow and the single-process flow: equal files prove the
+# single-process mode is equivalent to the per-stage flow, not merely
+# that it runs to completion. check_same.sh takes file pairs:
+# file_a file_b ... (.sdc pair first: check_same.sh stops at a binary
+# diff, and the .sdc verdict should be reported before that).
+#
+# Known divergence, deliberately left failing so it gets root-caused
+# rather than papered over: from the grt stage on, the grt-stage
+# repair_timing inserts one extra buffer (8 vs 7 on asap7/gcd) when the
+# process continues from the in-memory CTS state instead of reloading
+# 4_cts.odb, even though the 4_cts.odb/.sdc it starts from are
+# byte-identical (all .sdc match through the whole flow).
+[
+    sh_test(
+        name = "gcd_single_flow_{}_test".format(stage),
+        srcs = ["@openroad//test/orfs:check_same.sh"],
+        args = [
+            arg
+            for ext in [
+                "sdc",
+                "odb",
+            ]
+            for arg in [
+                "$(location :gcd_base_{}_{})".format(stage, ext),
+                "$(location :results/asap7/gcd/single/{}.{})".format(stem, ext),
+            ]
+        ],
+        data = [
+            ":gcd_base_{}_{}".format(stage, ext)
+            for ext in [
+                "sdc",
+                "odb",
+            ]
+        ] + [
+            ":results/asap7/gcd/single/{}.{}".format(stem, ext)
+            for ext in [
+                "sdc",
+                "odb",
+            ]
+        ],
+        tags = ["orfs"],
+    )
+    for stage, stem in SINGLE_FLOW_STAGES.items()
+]
+
+test_suite(
+    name = "gcd_single_flow_test",
+    tests = [
+        ":gcd_single_flow_{}_test".format(stage)
+        for stage in SINGLE_FLOW_STAGES
+    ],
+)
diff --git a/flow/designs/asap7/gcd/single_flow.tcl b/flow/designs/asap7/gcd/single_flow.tcl
new file mode 100644
index 0000000000..64fe2466b5
--- /dev/null
+++ b/flow/designs/asap7/gcd/single_flow.tcl
@@ -0,0 +1,10 @@
+# Seed this variant's results dir with the synthesis outputs, then run
+# the whole flow in this single OpenROAD process. Under bazel-orfs the
+# synthesis results are staged in the src stage's variant folder and
+# exposed via ODB_FILE, while RESULTS_DIR points at this run's own
+# variant folder.
+file mkdir $::env(RESULTS_DIR)
+file copy -force $::env(ODB_FILE) $::env(RESULTS_DIR)/1_synth.odb
+file copy -force [file rootname $::env(ODB_FILE)].sdc $::env(RESULTS_DIR)/1_synth.sdc
+
+source $::env(SCRIPTS_DIR)/flow.tcl
diff --git a/flow/scripts/flow.tcl b/flow/scripts/flow.tcl
new file mode 100644
index 0000000000..400b172981
--- /dev/null
+++ b/flow/scripts/flow.tcl
@@ -0,0 +1,41 @@
+# Runs all OpenROAD stages of the flow, from 1_synth.odb/.sdc through
+# the final report, in a single OpenROAD process. Produces the same
+# .odb/.sdc files in $RESULTS_DIR as the stage-per-process make flow:
+# the file copy -force lines mirror the Makefile do-copy recipes.
+
+# Enable keeping variables between stages
+set ::env(KEEP_VARS) 1
+
+# Floorplan
+source $::env(SCRIPTS_DIR)/floorplan.tcl
+source $::env(SCRIPTS_DIR)/macro_place.tcl
+source $::env(SCRIPTS_DIR)/tapcell.tcl
+source $::env(SCRIPTS_DIR)/pdn.tcl
+file copy -force $::env(RESULTS_DIR)/2_4_floorplan_pdn.odb $::env(RESULTS_DIR)/2_floorplan.odb
+file copy -force $::env(RESULTS_DIR)/2_1_floorplan.sdc $::env(RESULTS_DIR)/2_floorplan.sdc
+
+# Place
+source $::env(SCRIPTS_DIR)/global_place_skip_io.tcl
+source $::env(SCRIPTS_DIR)/io_placement.tcl
+source $::env(SCRIPTS_DIR)/global_place.tcl
+source $::env(SCRIPTS_DIR)/resize.tcl
+source $::env(SCRIPTS_DIR)/detail_place.tcl
+file copy -force $::env(RESULTS_DIR)/3_5_place_dp.odb $::env(RESULTS_DIR)/3_place.odb
+file copy -force $::env(RESULTS_DIR)/2_floorplan.sdc $::env(RESULTS_DIR)/3_place.sdc
+
+# CTS (cts.tcl itself writes 4_cts.sdc)
+source $::env(SCRIPTS_DIR)/cts.tcl
+file copy -force $::env(RESULTS_DIR)/4_1_cts.odb $::env(RESULTS_DIR)/4_cts.odb
+
+# Route
+source $::env(SCRIPTS_DIR)/global_route.tcl
+source $::env(SCRIPTS_DIR)/detail_route.tcl
+source $::env(SCRIPTS_DIR)/fillcell.tcl
+file copy -force $::env(RESULTS_DIR)/5_3_fillcell.odb $::env(RESULTS_DIR)/5_route.odb
+file copy -force $::env(RESULTS_DIR)/5_1_grt.sdc $::env(RESULTS_DIR)/5_route.sdc
+
+# Finish
+source $::env(SCRIPTS_DIR)/density_fill.tcl
+file copy -force $::env(RESULTS_DIR)/5_route.sdc $::env(RESULTS_DIR)/6_1_fill.sdc
+file copy -force $::env(RESULTS_DIR)/5_route.sdc $::env(RESULTS_DIR)/6_final.sdc
+source $::env(SCRIPTS_DIR)/final_report.tcl