diff --git a/Makefile b/Makefile
index 1e752b2a..5e6305c0 100644
--- a/Makefile
+++ b/Makefile
@@ -59,37 +59,46 @@ endif
 
 # Short fuzz smoke (extend FUZZTIME locally, e.g. FUZZTIME=30s make test-fuzz)
 FUZZTIME ?= 500ms
+# Route each fuzz invocation through a wrapper that tolerates the Go fuzz
+# engine's spurious "context deadline exceeded" at -fuzztime expiry
+# (golang/go#75804, Go 1.25-1.26.x). On Windows `go test` runs directly: local
+# fuzz smoke is short and a rare flake is cheap to re-run, and bash may be absent.
+ifeq ($(OS),Windows_NT)
+FUZZ_WRAPPER := $(GO) test
+else
+FUZZ_WRAPPER := bash scripts/fuzz-run.sh
+endif
 test-fuzz:
 	@echo "Fuzz smoke (FUZZTIME=$(FUZZTIME)) one target per line"
-	$(GO) test -fuzz=FuzzJSONRoundTrip$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/testkit
-	$(GO) test -fuzz=FuzzParseSnapshot$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/infra/modelcatalog/modelsdev
-	$(GO) test -fuzz=FuzzParseSelector$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/core/routing
-	$(GO) test -fuzz=FuzzParseSelectorFromBytes$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/core/routing
-	$(GO) test -fuzz=FuzzDecodeCreateRequest$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/frontends/openairesponses
-	$(GO) test -fuzz=FuzzDecodeMessageRequest$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/frontends/anthropic
-	$(GO) test -fuzz=FuzzDecodeGenerateContentRequest$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/frontends/gemini
-	$(GO) test -fuzz=FuzzDecodeChatRequest$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/frontends/openailegacy
-	$(GO) test -fuzz=FuzzWriteNonStreamJSON_toolArguments$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/frontends/anthropic
-	$(GO) test -fuzz=FuzzBuildGenerateContentResponse_toolJSON$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/frontends/gemini
-	$(GO) test -fuzz=FuzzCallValidateJSON$$ -fuzztime=$(FUZZTIME) -run=^$$ ./pkg/lipapi
-	$(GO) test -fuzz=FuzzMergeRouteQueryGenerationOptions$$ -fuzztime=$(FUZZTIME) -run=^$$ ./pkg/lipapi
-	$(GO) test -fuzz=FuzzCollectWithLimitsProgram$$ -fuzztime=$(FUZZTIME) -run=^$$ ./pkg/lipapi
-	$(GO) test -fuzz=FuzzStableCallIdentity$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/core/diag
-	$(GO) test -fuzz=FuzzParamsForCall$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/openairesponses
-	$(GO) test -fuzz=FuzzHandleResponseStreamUnion$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/openairesponses
-	$(GO) test -fuzz=FuzzBuildToolsParametersJSON$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/openairesponses
-	$(GO) test -fuzz=FuzzHandleMessageStreamEventUnion$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/protocols/anthropicmessages
-	$(GO) test -fuzz=FuzzToolInputSchemaParametersJSON$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/protocols/anthropicmessages
-	$(GO) test -fuzz=FuzzHandleChatCompletionChunk$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/openailegacy
-	$(GO) test -fuzz=FuzzBuildChatToolsParametersJSON$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/openailegacy
-	$(GO) test -fuzz=FuzzHandleGenerateContentResponse$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/protocols/geminigenerate
-	$(GO) test -fuzz=FuzzBuildToolsParametersJSON$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/protocols/geminigenerate
-	$(GO) test -fuzz=FuzzMessageToContentToolResultJSON$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/protocols/geminigenerate
-	$(GO) test -fuzz=FuzzAssistantPartsToContentBlocksJSON$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/bedrock
-	$(GO) test -fuzz=FuzzParseNDJSONLine$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/acp
-	$(GO) test -fuzz=FuzzMapSessionUpdateToEvents$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/acp
-	$(GO) test -fuzz=FuzzMergeHandshakeProfileExtensions$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/acp
-	$(GO) test -fuzz=FuzzHookMutationValidators$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/core/hooks
+	$(FUZZ_WRAPPER) -fuzz=FuzzJSONRoundTrip$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/testkit
+	$(FUZZ_WRAPPER) -fuzz=FuzzParseSnapshot$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/infra/modelcatalog/modelsdev
+	$(FUZZ_WRAPPER) -fuzz=FuzzParseSelector$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/core/routing
+	$(FUZZ_WRAPPER) -fuzz=FuzzParseSelectorFromBytes$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/core/routing
+	$(FUZZ_WRAPPER) -fuzz=FuzzDecodeCreateRequest$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/frontends/openairesponses
+	$(FUZZ_WRAPPER) -fuzz=FuzzDecodeMessageRequest$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/frontends/anthropic
+	$(FUZZ_WRAPPER) -fuzz=FuzzDecodeGenerateContentRequest$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/frontends/gemini
+	$(FUZZ_WRAPPER) -fuzz=FuzzDecodeChatRequest$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/frontends/openailegacy
+	$(FUZZ_WRAPPER) -fuzz=FuzzWriteNonStreamJSON_toolArguments$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/frontends/anthropic
+	$(FUZZ_WRAPPER) -fuzz=FuzzBuildGenerateContentResponse_toolJSON$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/frontends/gemini
+	$(FUZZ_WRAPPER) -fuzz=FuzzCallValidateJSON$$ -fuzztime=$(FUZZTIME) -run=^$$ ./pkg/lipapi
+	$(FUZZ_WRAPPER) -fuzz=FuzzMergeRouteQueryGenerationOptions$$ -fuzztime=$(FUZZTIME) -run=^$$ ./pkg/lipapi
+	$(FUZZ_WRAPPER) -fuzz=FuzzCollectWithLimitsProgram$$ -fuzztime=$(FUZZTIME) -run=^$$ ./pkg/lipapi
+	$(FUZZ_WRAPPER) -fuzz=FuzzStableCallIdentity$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/core/diag
+	$(FUZZ_WRAPPER) -fuzz=FuzzParamsForCall$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/openairesponses
+	$(FUZZ_WRAPPER) -fuzz=FuzzHandleResponseStreamUnion$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/openairesponses
+	$(FUZZ_WRAPPER) -fuzz=FuzzBuildToolsParametersJSON$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/openairesponses
+	$(FUZZ_WRAPPER) -fuzz=FuzzHandleMessageStreamEventUnion$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/protocols/anthropicmessages
+	$(FUZZ_WRAPPER) -fuzz=FuzzToolInputSchemaParametersJSON$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/protocols/anthropicmessages
+	$(FUZZ_WRAPPER) -fuzz=FuzzHandleChatCompletionChunk$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/openailegacy
+	$(FUZZ_WRAPPER) -fuzz=FuzzBuildChatToolsParametersJSON$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/openailegacy
+	$(FUZZ_WRAPPER) -fuzz=FuzzHandleGenerateContentResponse$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/protocols/geminigenerate
+	$(FUZZ_WRAPPER) -fuzz=FuzzBuildToolsParametersJSON$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/protocols/geminigenerate
+	$(FUZZ_WRAPPER) -fuzz=FuzzMessageToContentToolResultJSON$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/protocols/geminigenerate
+	$(FUZZ_WRAPPER) -fuzz=FuzzAssistantPartsToContentBlocksJSON$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/bedrock
+	$(FUZZ_WRAPPER) -fuzz=FuzzParseNDJSONLine$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/acp
+	$(FUZZ_WRAPPER) -fuzz=FuzzMapSessionUpdateToEvents$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/acp
+	$(FUZZ_WRAPPER) -fuzz=FuzzMergeHandshakeProfileExtensions$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/plugins/backends/acp
+	$(FUZZ_WRAPPER) -fuzz=FuzzHookMutationValidators$$ -fuzztime=$(FUZZTIME) -run=^$$ ./internal/core/hooks
 
 parity-checks:
 	$(GO) test $(GO_TEST_FLAGS) -tags=precommit,integration ./internal/testkit/conformance/...
diff --git a/internal/plugins/frontends/openaiwire/parts_test.go b/internal/plugins/frontends/openaiwire/parts_test.go
index dcc0db28..e85523f4 100644
--- a/internal/plugins/frontends/openaiwire/parts_test.go
+++ b/internal/plugins/frontends/openaiwire/parts_test.go
@@ -51,6 +51,17 @@ func TestFilePartFromBase64_pdfFilename(t *testing.T) {
 	}
 }
 
+func TestFilePartFromBase64_nonPdfFilename(t *testing.T) {
+	t.Parallel()
+	p := FilePartFromBase64("doc.txt", "qqq")
+	if p.FileMIME != "application/octet-stream" {
+		t.Fatalf("mime %q", p.FileMIME)
+	}
+	if p.Kind != lipapi.PartFileRef {
+		t.Fatalf("kind %v", p.Kind)
+	}
+}
+
 func TestImagePartFromURL_standardURL(t *testing.T) {
 	t.Parallel()
 	urlStr := "https://example.com/image.png"
diff --git a/scripts/fuzz-run.sh b/scripts/fuzz-run.sh
new file mode 100644
index 00000000..72d9c36b
--- /dev/null
+++ b/scripts/fuzz-run.sh
@@ -0,0 +1,54 @@
+#!/usr/bin/env bash
+# fuzz-run.sh — run a single `go test -fuzz=...` invocation and tolerate the
+# Go fuzz engine's known spurious "context deadline exceeded" failure that
+# occurs when -fuzztime expires (golang/go#75804, Go 1.25-1.26.x).
+#
+# At the -fuzztime boundary the fuzz coordinator cancels in-flight iterations
+# and may emit:
+#     --- FAIL: FuzzX (Ns)
+#         context deadline exceeded
+# with NO `file:line` reference and NO "Failing input written to" corpus entry.
+# That is the time budget expiring, not a real test failure.
+#
+# Real failures always include either a `..._test.go:<line>:` (or any
+# `*.go:<line>:`) reference or a "Failing input written to" line; those are
+# still surfaced as failures. Only the bare deadline message is tolerated.
+#
+# Usage: fuzz-run.sh <args passed to `go test -fuzz=...`>
+# Env:  GO — go binary (default: go)
+
+set -u
+
+GO_BIN="${GO:-go}"
+
+out="$(mktemp)"
+trap 'rm -f "$out"' EXIT
+
+# Note: no `set -e`/pipefail here — a nonzero `go test` exit is classified below.
+"$GO_BIN" test "$@" >"$out" 2>&1
+status=$?
+cat "$out"
+
+# Clean exit.
+if [ "$status" -eq 0 ]; then
+	exit 0
+fi
+
+# Real finding: a new failing corpus entry was written.
+if grep -q 'Failing input written to' "$out"; then
+	exit "$status"
+fi
+
+# Real assertion/panic failure: a source file:line reference is present.
+if grep -qE '\.go:[0-9]+:' "$out"; then
+	exit "$status"
+fi
+
+# Spurious engine deadline flake at the -fuzztime boundary — tolerate.
+if grep -q 'context deadline exceeded' "$out"; then
+	echo "fuzz-run: tolerated spurious Go fuzz engine 'context deadline exceeded' at -fuzztime boundary (golang/go#75804)" >&2
+	exit 0
+fi
+
+# Any other non-zero exit is a real error (build failure, panic w/o location, etc.).
+exit "$status"