diff --git a/changelog.d/gst-543-redact-diff-prefix.md b/changelog.d/gst-543-redact-diff-prefix.md
new file mode 100644
index 000000000..1b84077df
--- /dev/null
+++ b/changelog.d/gst-543-redact-diff-prefix.md
@@ -0,0 +1,5 @@
+**`gstack-redact` now catches a credential on an added diff line (GST-543).** The env.kv rule matched from the start of the line. On a unified-diff added line, the leading `+` blocked the match, so `git diff | gstack-redact` returned no finding and exit 0 for `+API_TOKEN=<random value>`. A `diff` code block in a PR body had the same blind spot. Pregate's `secrets` check and the pre-push hook were not affected, because both strip the `+` before scanning.
+
+### Fixed
+- **`lib/redact-patterns.ts`:** env.kv accepts one leading `+`, so the line in the example above now reports MEDIUM env.kv and exits 2. The name-shape check and the schema-field exemption accept the same prefix, so `API_TOKEN=changeme`, `cacheKey: …` and `input_key: …` stay clean on an added line, as they are without the prefix.
+- **`test/redact-diff-prefix.test.ts`:** each pattern in `PATTERNS` has a sample. The test requires it to report bare, behind `+`, `-` and a space, and on an added line inside a real hunk. A new pattern without a sample fails the test. The audit found env.kv was the only rule with the leading-`+` blind spot. Every other rule starts at a word boundary or has no anchor.
diff --git a/lib/redact-patterns.ts b/lib/redact-patterns.ts
index 330db6130..75d4a5fb6 100644
--- a/lib/redact-patterns.ts
+++ b/lib/redact-patterns.ts
@@ -121,7 +121,7 @@ export function shannonEntropy(s: string): number {
 //         (apiKey, authToken, clientSecret, stripeApiKey) — cacheKey/sortKey/
 //         monkey have no credential prefix and are rejected.
 const ENV_KV_NAME =
-  /^[ \t]*(?:export[ \t]+)?["']?([A-Za-z0-9_.-]*?(?:KEY|TOKEN|SECRET|PASSWORD|PASSWD|CREDENTIALS?|DSN|AUTH|COOKIE|SESSION|PRIVATE))["']?[ \t]*[:=]/i;
+  /^\+?[ \t]*(?:export[ \t]+)?["']?([A-Za-z0-9_.-]*?(?:KEY|TOKEN|SECRET|PASSWORD|PASSWD|CREDENTIALS?|DSN|AUTH|COOKIE|SESSION|PRIVATE))["']?[ \t]*[:=]/i;
 const ENV_KV_SUFFIX =
   /(KEY|TOKEN|SECRET|PASSWORD|PASSWD|CREDENTIALS?|DSN|AUTH|COOKIE|SESSION|PRIVATE)$/i;
 const ENV_KV_CRED_PREFIX =
@@ -656,7 +656,7 @@ const CALL_SHAPED_VALUE = /^[A-Za-z_$][\w$]*(?:\.[A-Za-z_$][\w$]*)*\(/;
  * A random key is mixed-case or one unbroken run, so it never takes this shape.
  */
 const SCHEMA_FIELD_NAME =
-  /^[ \t]*["']?(?:input|output|field|column|lookup|cache|sort|partition|range|index|row|group|join|property|metric|catalog|schema|translation|idempotency|dedup)[_.-]key["']?[ \t]*[:=]/;
+  /^\+?[ \t]*["']?(?:input|output|field|column|lookup|cache|sort|partition|range|index|row|group|join|property|metric|catalog|schema|translation|idempotency|dedup)[_.-]key["']?[ \t]*[:=]/;
 const SCHEMA_FIELD_VALUE = /^[a-z][a-z0-9]*(?:[_.-][a-z][a-z0-9]*)+$/;
 function isSchemaFieldIdentifier(span: string, match: RegExpExecArray): boolean {
   return SCHEMA_FIELD_NAME.test(match[0]) && SCHEMA_FIELD_VALUE.test(span);
@@ -962,7 +962,13 @@ export const PATTERNS: RedactPattern[] = [
     // (cacheKey:, sortKey:, monkey:) fires a MEDIUM confirm on entropic
     // values. The value must stay capture group 1 (the engine masks group 1),
     // so name-shape checking lives in validate, not in a second group.
-    regex: /^[ \t]*(?:export[ \t]+)?["']?[A-Za-z0-9_.-]*(?:KEY|TOKEN|SECRET|PASSWORD|PASSWD|CREDENTIALS?|DSN|AUTH|COOKIE|SESSION|PRIVATE)["']?[ \t]*[:=][ \t]*["']?([^\s'"]{8,})["']?/i,
+    // GST-543: an optional leading `+` is a unified-diff added line
+    // (`git diff | gstack-redact`, a diff fence in a PR body); without it the
+    // line anchor stopped at the prefix and an added credential went
+    // unreported. ENV_KV_NAME and SCHEMA_FIELD_NAME take the same prefix so
+    // the name-shape and schema exemptions hold on an added line. `-` and a
+    // space already match (`-` as a name character, a space as indentation).
+    regex: /^\+?[ \t]*(?:export[ \t]+)?["']?[A-Za-z0-9_.-]*(?:KEY|TOKEN|SECRET|PASSWORD|PASSWD|CREDENTIALS?|DSN|AUTH|COOKIE|SESSION|PRIVATE)["']?[ \t]*[:=][ \t]*["']?([^\s'"]{8,})["']?/i,
     // Only fire on credential-shaped names with high-entropy values — kills
     // `FOO_KEY=changeme` and `cacheKey: <entropic-id>` FPs. #2912: a value
     // that is exactly an environment read (`os.environ["X"]`,
diff --git a/test/redact-diff-prefix.test.ts b/test/redact-diff-prefix.test.ts
new file mode 100644
index 000000000..932622b71
--- /dev/null
+++ b/test/redact-diff-prefix.test.ts
@@ -0,0 +1,95 @@
+/**
+ * GST-543: a unified-diff line prefix never hides a finding. `git diff |
+ * gstack-redact` and a `\`\`\`diff` fence in a PR body put `+`, `-` or a space
+ * before every line; a line-anchored rule that stops at that character
+ * misses the credential on an added line. Every pattern must report its
+ * sample bare, behind each diff prefix and inside a real hunk.
+ */
+import { describe, expect, test } from "bun:test";
+import { spawnSync } from "node:child_process";
+import * as path from "node:path";
+import { scan } from "../lib/redact-engine";
+import { PATTERNS } from "../lib/redact-patterns";
+
+const j = (...p: string[]) => p.join("");
+const hex32 = "9f8e7d6c5b4a39281706f5e4d3c2b1a0";
+const SAMPLES: Record<string, string> = {
+  "aws.access_key": j("AKIA", "ZQ3XN7P2LM4RT8WV"),
+  "aws.secret_key": j("aws_secret_access_key = ", "Zq3Xn7P2Lm4Rt8Wv", "Bc5Df6Gh7Jk8Lm9Np0Qr1St2"),
+  "github.pat": j("ghp_", "a1B2c3D4e5F6g7H8i9J0k1L2m3N4o5P6q7R8"),
+  "github.oauth": j("gho_", "a1B2c3D4e5F6g7H8i9J0k1L2m3N4o5P6q7R8"),
+  "github.server": j("ghs_", "a1B2c3D4e5F6g7H8i9J0k1L2m3N4o5P6q7R8"),
+  "github.fine_grained": j("github_pat_", "a1B2c3D4e5F6g7H8i9J0".repeat(4), "kL"),
+  "gitlab.token": j("glpat-", "a1B2c3D4e5F6g7H8i9J0"),
+  "groq.key": j("gsk_", "a1B2c3D4e5F6g7H8i9J0k1L2"),
+  "tavily.key": j("tvly-", "a1B2c3D4e5F6g7H8i9J0"),
+  "notion.token": j("ntn_", "a1B2c3D4e5F6g7H8i9J0k1L2m3N4o5P6q7R8s9T0u1V2"),
+  "huggingface.token": j("hf_", "a1B2c3D4e5F6g7H8i9J0k1L2m3N4o5P6"),
+  "npm.token": j("npm_", "a1B2c3D4e5F6g7H8i9J0k1L2m3N4o5P6q7R8"),
+  "digitalocean.token": j("dop_v1_", hex32, hex32),
+  "gcp.service_account": j('{"private_key_id": "', hex32, '", "private_key": "-----BEGIN ', 'PRIVATE KEY-----"}'),
+  "anthropic.key": j("sk-ant-", "api03-a1B2c3D4e5F6g7H8i9J0k1L2"),
+  "openai.key": j("sk-proj-", "a1B2c3D4e5F6g7H8i9J0k1L2m3N4o5P6q7R8s9T0u1V2w3X4"),
+  "sendgrid.key": j("SG.", "a1B2c3D4e5F6g7H8i9J0k1", ".", "a1B2c3D4e5F6g7H8i9J0k1L2m3N4o5P6q7R8s9T0u1V"),
+  "stripe.secret": j("sk_live_", "a1B2c3D4e5F6g7H8i9J0k1L2"),
+  "slack.token": j("xoxb-", "12345", "67890-a1B2c3D4e5F6"),
+  "slack.webhook": j("https://hooks.slack.com/services/", "T0ABCDEFG/B0ABCDEFG/", "a1B2c3D4e5F6g7H8i9J0k1L2"),
+  "discord.webhook": j("https://discord.com/api/webhooks/", "123456789012345678/", "a1B2c3D4e5F6g7H8i9J0k1L2m3N4o5P6q7R8s9T0u1V2w3X4y5Z6a7B8c9D0e1F2"),
+  "twilio.auth_token": j("AC", hex32, " ", hex32.split("").reverse().join("")),
+  "google.oauth_client_secret": j("GOCSPX-", "a1B2c3D4e5F6g7H8i9J0k1L2"),
+  "telegram.bot_token": j("123456789", ":", "AAa1B2c3D4e5F6g7H8i9J0k1L2m3N4o5P6q"),
+  "pem.private_key": j("-----BEGIN RSA ", "PRIVATE KEY-----"),
+  "db.url_with_password": j("postgres://admin:", "Xk9pQ2vLm7Rt", "@db.acme.io/prod"),
+  "creds.basic_auth_url": j("https://deploy:", "Xk9pQ2vLm7Rt", "@ci.acme.io/hook"),
+  "stripe.publishable": j("pk_live_", "a1B2c3D4e5F6g7H8i9J0k1L2"),
+  "google.api_key": j("AIza", "SyA1b2C3d4E5f6G7h8I9j0K1l2M3n4O5p6Q"),
+  "jwt": ["eyJhbGciOiJIUzI1NiJ9", "eyJzdWIiOiIxMjM0NTY3ODkwIn0", "dozjgNryP4J3jVmNHl0w5N_XgL0n3I9PlFUP0THsR8U"].join("."),
+  "env.kv": j("API_TOKEN=", "8Fk2pQ9vXz4wL7mN3rT6yB1cD5eG0hJ"),
+  "auth.bearer": j("Authorization: Bearer ", "a1B2c3D4e5F6g7H8i9J0k1L2"),
+  "pii.email": j("dana.whitfield@", "acmecorp.io"),
+  "pii.phone.e164": j("+1415", "5552671"),
+  "pii.ssn": j("123-45", "-6789"),
+  "pii.cc": j("4532 0151 ", "1283 0366"),
+  "pii.ip_public": j("203.0.", "113.77"),
+  "pii.wallet": j("0x529084000985", "27886E0F7030069857D2E4169EE7"),
+  "internal.hostname": j("build-01.", "corp"),
+  "internal.url_private": j("http://local", "host:8080/admin"),
+  "legal.nda_marker": j("CONFIDEN", "TIAL"),
+  "legal.named_criticism": j("Dana Whitfield was ", "fir", "ed"),
+  "internal.user_path": j("/Us", "ers/dana/projects/app"),
+  "hygiene.todo": j("TO", "DO(dana)"),
+};
+
+const ids = (text: string) => scan(text, { repoVisibility: "public", processEnv: {} }).findings.map((f) => f.id);
+const hunk = (body: string) => ["diff --git a/x b/x", "--- a/x", "+++ b/x", "@@ -0,0 +1 @@", body, ""].join("\n");
+
+describe("GST-543: a diff line prefix never hides a finding", () => {
+  test("every pattern has a sample that reports bare", () => {
+    expect(PATTERNS.map((p) => p.id).filter((id) => !SAMPLES[id])).toEqual([]);
+    expect(PATTERNS.filter((p) => !ids(SAMPLES[p.id]!).includes(p.id)).map((p) => p.id)).toEqual([]);
+  });
+
+  test("each sample still reports behind +, - and a space, and on an added line inside a hunk", () => {
+    const missed: string[] = [];
+    for (const p of PATTERNS) {
+      const s = SAMPLES[p.id]!;
+      for (const [label, text] of [["+", "+" + s], ["-", "-" + s], ["space", " " + s], ["hunk", hunk("+" + s)], ["indented hunk", hunk("+    " + s)]] as const)
+        if (!ids(text).includes(p.id)) missed.push(`${p.id} (${label})`);
+    }
+    expect(missed).toEqual([]);
+  });
+
+  test("git diff | gstack-redact reports an added env.kv credential and exits 2; a placeholder on the same line stays clean", () => {
+    const run = (line: string) => spawnSync("bun", [path.join(import.meta.dir, "..", "bin", "gstack-redact"), "--json"], { input: hunk("+" + line), encoding: "utf8", timeout: 30_000 });
+    const real = run(SAMPLES["env.kv"]!);
+    expect({ status: real.status, ids: JSON.parse(real.stdout).findings.map((f: { id: string }) => f.id) }).toEqual({ status: 2, ids: ["env.kv"] });
+    expect(run("API_TOKEN=changeme").status).toBe(0);
+  });
+
+  test("the prefix changes nothing else: env.kv's exemptions hold on an added line", () => {
+    for (const line of ["API_TOKEN=changeme", "cacheKey: 8Fk2pQ9vXz4wL7mN3rT6yB1cD5eG0hJ", "input_key: expected_media_rate_bits_per_second", 'api_key=os.environ["API_KEY"]', "TOKEN=${API_TOKEN}"]) {
+      expect({ line, bare: ids(line).includes("env.kv") }).toEqual({ line, bare: false });
+      expect({ line, added: ids(hunk("+" + line)).includes("env.kv") }).toEqual({ line, added: false });
+    }
+  });
+});