diff --git a/src/vizier/services/adaptive_export/internal/sink/BUILD.bazel b/src/vizier/services/adaptive_export/internal/sink/BUILD.bazel
index ff1bda207b5..10015b1550a 100644
--- a/src/vizier/services/adaptive_export/internal/sink/BUILD.bazel
+++ b/src/vizier/services/adaptive_export/internal/sink/BUILD.bazel
@@ -36,6 +36,7 @@ pl_go_test(
     name = "sink_test",
     srcs = [
         "clickhouse_test.go",
+        "content_type_contract_test.go",
         "encode_bench_test.go",
         "fastencode_test.go",
     ],
diff --git a/src/vizier/services/adaptive_export/internal/sink/content_type_contract_test.go b/src/vizier/services/adaptive_export/internal/sink/content_type_contract_test.go
new file mode 100644
index 00000000000..24e385bd384
--- /dev/null
+++ b/src/vizier/services/adaptive_export/internal/sink/content_type_contract_test.go
@@ -0,0 +1,262 @@
+// Copyright 2018- The Pixie Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package sink
+
+import (
+	"bufio"
+	"bytes"
+	"context"
+	"encoding/json"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"regexp"
+	"strings"
+	"testing"
+
+	"px.dev/pixie/src/vizier/services/adaptive_export/internal/clickhouse"
+)
+
+// I1 — schema invariant.
+//
+// Parses the embedded schema.sql, walks every CREATE TABLE block,
+// and asserts that any column named `content_type` is declared as
+// `Int64` (case-sensitive; CH is). Catches a future PR that
+// "improves" the column to String / Nullable(Int64) / etc. without
+// updating the encoder side.
+func TestContract_ContentTypeIsInt64InSchema(t *testing.T) {
+	// Reach the canonical schema via the public DDL(table) API so this
+	// test stays decoupled from the embed-internal var name.
+	type col struct {
+		table string
+		typ   string
+	}
+	var found []col
+	colRE := regexp.MustCompile(`(?m)^\s*content_type\s+([A-Za-z0-9_()]+)`)
+	for _, table := range clickhouse.PixieTables() {
+		ddl, err := clickhouse.DDL(table)
+		if err != nil {
+			t.Fatalf("DDL(%q): %v", table, err)
+		}
+		if m := colRE.FindStringSubmatch(ddl); m != nil {
+			found = append(found, col{table: table, typ: strings.TrimRight(m[1], ",")})
+		}
+	}
+	if len(found) == 0 {
+		t.Fatalf("no content_type column found in PixieTables — did the column get renamed? Audit the encoder side too.")
+	}
+	for _, c := range found {
+		if c.typ != "Int64" {
+			t.Fatalf("schema drift: %s.content_type is %q, want Int64. CH input_format_skip_unknown_fields=1 will silent-drop encoder mismatches. Update encoder side together if intentional.", c.table, c.typ)
+		}
+	}
+	t.Logf("invariant I1 holds across %d tables: %v", len(found), found)
+}
+
+// I2 — encoder invariant.
+//
+// Drives fastencode directly with content_type as int64 (the canonical
+// shape Pixie's stirling http parser emits) and parses the emitted
+// NDJSON to confirm the value is a JSON NUMBER, not a string. Also
+// guards the int conversion path by feeding int / int32 / int64 / a
+// json.Number and asserting each lands as a JSON number too.
+func TestContract_FastEncodeContentTypeAsInt(t *testing.T) {
+	cases := []struct {
+		name string
+		v    any
+	}{
+		{"int64", int64(2)},
+		{"int32", int32(2)},
+		{"int", 2},
+		{"json.Number", json.Number("2")},
+	}
+	cols := minHTTPRowCols()
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			row := canonicalHTTPRow()
+			row["content_type"] = c.v
+			var buf bytes.Buffer
+			// stage the fast-path column cache the same way production
+			// does via clickhouse.Columns — we don't reach into the
+			// package-private cache; encodePixieRowsFast already does
+			// the lookup itself.
+			if err := encodePixieRowsFast(&buf, "http_events", []map[string]any{row}); err != nil {
+				t.Fatalf("encodePixieRowsFast: %v", err)
+			}
+			line := strings.TrimSpace(buf.String())
+			// Parse with json.Decoder + UseNumber so we see whether the
+			// emitter wrote "content_type":2 (number) vs "2" (string).
+			d := json.NewDecoder(strings.NewReader(line))
+			d.UseNumber()
+			var parsed map[string]any
+			if err := d.Decode(&parsed); err != nil {
+				t.Fatalf("decode emitted line: %v\nline=%s", err, line)
+			}
+			ct, ok := parsed["content_type"]
+			if !ok {
+				t.Fatalf("emitted line missing content_type; line=%s", line)
+			}
+			if _, isNum := ct.(json.Number); !isNum {
+				t.Fatalf("content_type emitted as %T (%v), want JSON number — CH would silent-drop a non-number into an Int64 column. line=%s", ct, ct, line)
+			}
+			_ = cols
+		})
+	}
+}
+
+// I3 — silent-drop must be loud.
+//
+// A no-op CH that returns 200 OK + X-ClickHouse-Summary written_rows=0
+// against a non-empty body. The sink must surface this as an error.
+func TestContract_SilentDropDetected(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		_, _ = io.Copy(io.Discard, r.Body)
+		w.Header().Set("X-ClickHouse-Summary", `{"read_rows":"0","read_bytes":"0","written_rows":"0","written_bytes":"0"}`)
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer srv.Close()
+
+	s, err := New(Config{Endpoint: srv.URL})
+	if err != nil {
+		t.Fatalf("New: %v", err)
+	}
+	err = s.WritePixieRows(context.Background(), "http_events", []map[string]any{canonicalHTTPRow()})
+	if err == nil {
+		t.Fatalf("WritePixieRows returned nil on written_rows=0 reply — silent-drop detection is broken")
+	}
+	if !strings.Contains(err.Error(), "silent drop") {
+		t.Fatalf("error %q does not mention 'silent drop' — runbook-grep will miss it", err.Error())
+	}
+}
+
+// I3.b — sibling guard: when CH reports written_rows >= rows_sent the
+// sink must NOT error. Pins the parse so a future refactor doesn't
+// over-trigger and false-positive every successful write.
+func TestContract_SilentDropNotTriggeredOnSuccess(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		_, _ = io.Copy(io.Discard, r.Body)
+		w.Header().Set("X-ClickHouse-Summary", `{"written_rows":"1"}`)
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer srv.Close()
+	s, _ := New(Config{Endpoint: srv.URL})
+	if err := s.WritePixieRows(context.Background(), "http_events", []map[string]any{canonicalHTTPRow()}); err != nil {
+		t.Fatalf("WritePixieRows errored on success summary: %v", err)
+	}
+}
+
+// I3.c — header absence is tolerated (older CH versions / proxies
+// strip it). Documents the policy decision so a future "tighten the
+// gate" PR doesn't break clusters running CH 22.x.
+func TestContract_SilentDropToleratesMissingSummaryHeader(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		_, _ = io.Copy(io.Discard, r.Body)
+		// no X-ClickHouse-Summary header
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer srv.Close()
+	s, _ := New(Config{Endpoint: srv.URL})
+	if err := s.WritePixieRows(context.Background(), "http_events", []map[string]any{canonicalHTTPRow()}); err != nil {
+		t.Fatalf("WritePixieRows errored on missing summary header: %v (policy is tolerate-missing)", err)
+	}
+}
+
+// I4 — round-trip an http_events row through WritePixieRows against a
+// recording httptest CH; assert the on-wire body has content_type as
+// a number, the INSERT targets the right table, and the body is
+// one NDJSON object per row.
+func TestContract_HTTPEventsRoundTrip(t *testing.T) {
+	var gotQuery, gotBody string
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		gotQuery = r.URL.Query().Get("query")
+		b, _ := io.ReadAll(r.Body)
+		gotBody = string(b)
+		// echo back a successful summary so the silent-drop guard is satisfied
+		w.Header().Set("X-ClickHouse-Summary", `{"written_rows":"1"}`)
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer srv.Close()
+
+	s, _ := New(Config{Endpoint: srv.URL})
+	if err := s.WritePixieRows(context.Background(), "http_events", []map[string]any{canonicalHTTPRow()}); err != nil {
+		t.Fatalf("WritePixieRows: %v", err)
+	}
+	if !strings.Contains(gotQuery, "INSERT INTO ") {
+		t.Fatalf("query missing INSERT INTO; got %q", gotQuery)
+	}
+	if !strings.Contains(gotQuery, "http_events") {
+		t.Fatalf("query doesn't target http_events; got %q", gotQuery)
+	}
+	if !strings.Contains(gotQuery, "FORMAT JSONEachRow") {
+		t.Fatalf("query missing FORMAT JSONEachRow; got %q", gotQuery)
+	}
+	if !strings.Contains(gotBody, `"content_type":2`) {
+		t.Fatalf("body has content_type as non-number (CH would silent-drop). body=%s", gotBody)
+	}
+	// One NDJSON line per row → exactly one newline-trailing object here.
+	sc := bufio.NewScanner(strings.NewReader(strings.TrimRight(gotBody, "\n")))
+	n := 0
+	for sc.Scan() {
+		n++
+	}
+	if n != 1 {
+		t.Fatalf("body has %d NDJSON lines, want 1; body=%s", n, gotBody)
+	}
+}
+
+// canonicalHTTPRow returns a row whose shape matches what
+// fastencode would see from a pxapi http_events read. Any new
+// schema column added must be appended here too — the test will
+// fail with a clear "schema added X column; canonical row needs
+// it" message if a missing column hits errFastEncodeUnsupported.
+func canonicalHTTPRow() map[string]any {
+	return map[string]any{
+		"time_":          int64(1_717_200_000_000_000_000),
+		"upid":           "00000000-0000-0000-0000-000000000001",
+		"namespace":      "redis",
+		"pod":            "redis-578d5dc9bd-kjj78",
+		"remote_addr":    "10.0.0.1",
+		"remote_port":    int64(443),
+		"local_addr":     "10.0.0.2",
+		"local_port":     int64(48000),
+		"trace_role":     int64(1),
+		"encrypted":      int64(0),
+		"major_version":  int64(1),
+		"minor_version":  int64(1),
+		"content_type":   int64(2), // JSON — the schema-honest int
+		"req_headers":    `{"User-Agent":"curl/8"}`,
+		"req_method":     "GET",
+		"req_path":       "/x",
+		"req_body":       "",
+		"req_body_size":  int64(0),
+		"resp_headers":   `{"Content-Type":"application/json"}`,
+		"resp_status":    int64(200),
+		"resp_message":   "OK",
+		"resp_body":      "{}",
+		"resp_body_size": int64(2),
+		"latency":        int64(123_456),
+		"hostname":       "node-1",
+	}
+}
+
+// minHTTPRowCols is the small fixed column list any "is it int?"
+// micro-check uses; kept aligned with the canonical row above so
+// schema additions surface as a missing-column in the canonical row,
+// not a flaky test.
+func minHTTPRowCols() []string {
+	return []string{"content_type", "remote_port", "local_port", "trace_role", "encrypted", "major_version", "minor_version", "resp_status", "latency", "req_body_size", "resp_body_size"}
+}