diff --git a/lab/internal/harness/harness_cache_test.go b/lab/internal/harness/harness_cache_test.go
index 948bafc..801890c 100644
--- a/lab/internal/harness/harness_cache_test.go
+++ b/lab/internal/harness/harness_cache_test.go
@@ -63,8 +63,8 @@ func TestHarnessCacheReachesCodexCodingInvocation(t *testing.T) {
 	if !reflect.DeepEqual(plainEnv, []string{"GOCACHE=/user/go-build", "GOMODCACHE=/user/mod", "GOTMPDIR=/user/gotmp"}) {
 		t.Fatalf("a coding run without the cache changed the environment: %q", plainEnv)
 	}
-	if slices.Contains(plainArgv, "--add-dir") {
-		t.Fatalf("a coding run without the cache got --add-dir: %q", plainArgv)
+	if slices.Contains(plainArgv, "--add-dir") || slices.ContainsFunc(plainArgv, func(a string) bool { return strings.HasPrefix(a, "shell_environment_policy.") }) {
+		t.Fatalf("a coding run without the cache got --add-dir or a policy override: %q", plainArgv)
 	}
 	cachedArgv, cachedEnv := runCodexEcho(t, WithHarnessCache(request, root), base)
 	want := []string{"GOCACHE=" + filepath.Join(root, "go-build"), "GOMODCACHE=/user/mod", "GOTMPDIR=" + filepath.Join(root, "gotmp")}
@@ -78,9 +78,51 @@ func TestHarnessCacheReachesCodexCodingInvocation(t *testing.T) {
 	if cachedArgv[len(cachedArgv)-1] != "-" || cachedArgv[slices.Index(cachedArgv, "--sandbox")+1] != "workspace-write" {
 		t.Fatalf("sandbox or stdin argument changed: %q", cachedArgv)
 	}
-	stripped := slices.Delete(slices.Clone(cachedArgv), i, i+2)
+	overrides := []string{
+		"-c", `shell_environment_policy.set.GOCACHE="` + filepath.Join(root, "go-build") + `"`,
+		"-c", `shell_environment_policy.set.GOTMPDIR="` + filepath.Join(root, "gotmp") + `"`,
+	}
+	if i+2+len(overrides) > len(cachedArgv) || !reflect.DeepEqual(cachedArgv[i+2:i+2+len(overrides)], overrides) {
+		t.Fatalf("argv lacks the shell_environment_policy overrides %q: %q", overrides, cachedArgv)
+	}
+	stripped := slices.Delete(slices.Clone(cachedArgv), i, i+2+len(overrides))
 	if !reflect.DeepEqual(withoutOutputPaths(stripped), withoutOutputPaths(plainArgv)) {
-		t.Fatalf("argv differs beyond --add-dir:\n%q\n%q", stripped, plainArgv)
+		t.Fatalf("argv differs beyond --add-dir and the overrides:\n%q\n%q", stripped, plainArgv)
+	}
+}
+
+func TestHarnessCacheOverridesQuoteTheRoot(t *testing.T) {
+	for _, c := range []struct{ root, gocache, gotmpdir string }{
+		{`/lab/a"b`, `"/lab/a\"b/go-build"`, `"/lab/a\"b/gotmp"`},
+		{`/lab/a\b`, `"/lab/a\\b/go-build"`, `"/lab/a\\b/gotmp"`},
+		{`/lab/a\"b`, `"/lab/a\\\"b/go-build"`, `"/lab/a\\\"b/gotmp"`},
+	} {
+		call, err := BuildInvocation("codex", WithHarnessCache(map[string]any{"kind": "molecule"}, c.root), "/fixture/result")
+		if err != nil {
+			t.Fatalf("%q: %v", c.root, err)
+		}
+		for _, want := range []string{"shell_environment_policy.set.GOCACHE=" + c.gocache, "shell_environment_policy.set.GOTMPDIR=" + c.gotmpdir} {
+			if i := slices.Index(call.Args, want); i < 1 || call.Args[i-1] != "-c" {
+				t.Fatalf("%q: argv lacks -c %s: %q", c.root, want, call.Args)
+			}
+		}
+	}
+}
+
+func TestHarnessCacheOverridesRefuseANewline(t *testing.T) {
+	for _, s := range []string{"/lab/a\nb", "/lab/a\rb"} {
+		if _, err := tomlBasicString(s); err == nil {
+			t.Fatalf("quoted %q", s)
+		}
+		if _, err := codexHarnessCacheOverrides(s); err == nil {
+			t.Fatalf("built overrides for %q", s)
+		}
+		if _, err := BuildInvocation("codex", WithHarnessCache(map[string]any{"kind": "molecule"}, s), "/fixture/result"); err == nil {
+			t.Fatalf("built an invocation for %q", s)
+		}
+	}
+	if got, err := tomlBasicString(`/lab/plain`); err != nil || got != `"/lab/plain"` {
+		t.Fatalf("plain path quoted as %q, %v", got, err)
 	}
 }
 
diff --git a/lab/internal/harness/isolation_test.go b/lab/internal/harness/isolation_test.go
index 268b003..a504e84 100644
--- a/lab/internal/harness/isolation_test.go
+++ b/lab/internal/harness/isolation_test.go
@@ -587,6 +587,12 @@ func TestAdapterIsolationReport(t *testing.T) {
 			t.Fatalf("the claude-code reason omits %q: %s", mention, claude)
 		}
 	}
+	codex := AdapterIsolation("codex").Reason
+	for _, mention := range []string{"shell_environment_policy.set.GOCACHE", "GOTMPDIR"} {
+		if !strings.Contains(codex, mention) {
+			t.Fatalf("the codex reason omits %q: %s", mention, codex)
+		}
+	}
 	native := []string{"/forgecell", "__adapter", "claude-code", "/claude"}
 	if got := BindingIsolation(native); got != AdapterIsolation("claude-code") {
 		t.Fatalf("%+v", got)
diff --git a/lab/internal/harness/protocol.go b/lab/internal/harness/protocol.go
index 0cf40fb..76e595d 100644
--- a/lab/internal/harness/protocol.go
+++ b/lab/internal/harness/protocol.go
@@ -8,6 +8,7 @@ import (
 	"github.com/DanielNetzer/forgecell/lab/internal/formula"
 	"github.com/DanielNetzer/forgecell/lab/internal/process"
 	"github.com/DanielNetzer/forgecell/lab/internal/readiness"
+	"github.com/DanielNetzer/forgecell/lab/internal/resources"
 	"io"
 	"maps"
 	"math"
@@ -35,7 +36,9 @@ const analysisInstruction = "You are assessing ticket readiness during the intak
 // reviewedAcceptance empty.
 // Version 8 reads the Lab-owned harness Go cache (harnessGoCache) on a Codex coding
 // request: --add-dir names it, and GOCACHE and GOTMPDIR point into it.
-const AdapterProtocolVersion = "8"
+// Version 9 also sets GOCACHE and GOTMPDIR through shell_environment_policy.set
+// overrides, which the user's Codex shell_environment_policy cannot filter.
+const AdapterProtocolVersion = "9"
 
 // harnessCacheRequestKey carries the root of the Lab-owned harness Go cache in a Codex
 // coding request. Like harnessModel it is private to the Lab and never reaches the
@@ -56,6 +59,31 @@ func requestHarnessCache(request map[string]any) (string, error) {
 	return root, nil
 }
 
+// tomlBasicString quotes s as a TOML basic string, escaping backslash and double quote.
+// A newline cannot be written into a single-line override, so it is refused.
+func tomlBasicString(s string) (string, error) {
+	if strings.ContainsAny(s, "\r\n") {
+		return "", fmt.Errorf("a newline cannot be quoted in a Codex config override")
+	}
+	return `"` + strings.NewReplacer(`\`, `\\`, `"`, `\"`).Replace(s) + `"`, nil
+}
+
+// codexHarnessCacheOverrides returns the -c overrides that set GOCACHE and GOTMPDIR for
+// every command Codex runs. shell_environment_policy.set applies after inherit and the
+// include and exclude filters, so the user's policy cannot drop them.
+func codexHarnessCacheOverrides(root string) ([]string, error) {
+	cache := resources.HarnessCacheAt(root)
+	var args []string
+	for _, v := range []struct{ name, path string }{{"GOCACHE", cache.BuildCache}, {"GOTMPDIR", cache.TmpDir}} {
+		quoted, err := tomlBasicString(v.path)
+		if err != nil {
+			return nil, err
+		}
+		args = append(args, "-c", "shell_environment_policy.set."+v.name+"="+quoted)
+	}
+	return args, nil
+}
+
 // WithHarnessCache returns the request with the harness Go cache root attached, or the
 // request itself when root is empty. The caller's map is never modified. BuildInvocation
 // accepts it only on a Codex coding request.
@@ -292,7 +320,7 @@ func AdapterIsolation(id string) Isolation {
 	case "claude-code":
 		return Isolation{IsolationPartial, "Coding, formula-improvement and analysis with extensions run with --setting-sources project; analysis and review without extensions run with --safe-mode; MCP servers are limited to the Lab-approved set (--strict-mcp-config). User settings, plugins and hooks are excluded, so user hooks that rewrite tool output no longer change what the harness sees (observed in a live probe of --setting-sources user versus project). Not verified, hence partial: managed (enterprise) policy settings, and whether a user-level CLAUDE.md, user agents or user skills still load under --setting-sources project. Project .claude/settings.json can still load: it is fingerprinted from the base commit, a coding or formula-improvement run is refused when .claude holds settings, hooks or agents, and a coding run that changes .claude fails as a scope violation."}
 	case "codex":
-		return Isolation{IsolationPartial, "Codex coding and formula-improvement runs still read the user's CODEX_HOME/config.toml (profiles, hooks, MCP servers); they run with approval_policy never and a sandbox, and config.toml is fingerprinted. Analysis and review add --strict-config, --ignore-rules and disable shell, plugins and hooks. A pinned model is not supported."}
+		return Isolation{IsolationPartial, "Codex coding and formula-improvement runs still read the user's CODEX_HOME/config.toml (profiles, hooks, MCP servers); they run with approval_policy never and a sandbox, and config.toml is fingerprinted. Coding runs with the Lab-owned Go cache override shell_environment_policy.set.GOCACHE and GOTMPDIR, so the user's shell_environment_policy cannot drop them. Analysis and review add --strict-config, --ignore-rules and disable shell, plugins and hooks. A pinned model is not supported."}
 	case "cursor":
 		return Isolation{IsolationUnknown, "Cursor Agent's user configuration (rules, MCP servers, plugins, hooks) is not verified to be excluded: runs only pass --sandbox enabled and --trust (and --mode ask for formula-improvement), and no Cursor configuration is fingerprinted. Analysis and review are unavailable. A pinned model is not supported."}
 	}
@@ -443,8 +471,14 @@ func BuildInvocation(id string, request map[string]any, output string) (Invocati
 			}
 		}
 		if cache != "" {
-			// The workspace-write sandbox may also write exactly the Lab-owned cache.
+			// The workspace-write sandbox may also write exactly the Lab-owned cache, and
+			// every command Codex runs is pointed at it.
+			overrides, err := codexHarnessCacheOverrides(cache)
+			if err != nil {
+				return Invocation{}, err
+			}
 			result.Args = append(result.Args, "--add-dir", cache)
+			result.Args = append(result.Args, overrides...)
 		}
 		result.Args = append(result.Args, "-")
 	case "claude-code":
diff --git a/lab/internal/harness/protocol_contract_test.go b/lab/internal/harness/protocol_contract_test.go
index 3db5500..1ca898c 100644
--- a/lab/internal/harness/protocol_contract_test.go
+++ b/lab/internal/harness/protocol_contract_test.go
@@ -20,6 +20,7 @@ var adapterContractDigests = map[string]string{
 	"6": "65f4a5f18b8bcdcd538ab3ac5ce44c26de3fd62ebd07c8577f3413f14fc0e2fb",
 	"7": "9a2549ee76ecae7395ab23915224d6294bd4ad8e46ca326f83ea6b0692da0d69",
 	"8": "df91601b9703e2a050087e824b5106cdb54fba19adbd3f4a86c9ea34a365b4bd",
+	"9": "4d29883a0a8602024f44e7031fd4e72bda1845992dcaa6d2c6177c101548d8de",
 }
 
 func adapterContractDigest(t *testing.T) string {