diff --git a/docs/agent-environments.md b/docs/agent-environments.md
index 97e6812cb9..0c7c83197a 100644
--- a/docs/agent-environments.md
+++ b/docs/agent-environments.md
@@ -186,7 +186,8 @@ connecting to `/mcp`:
 `capabilities.tools` lists the same names, descriptions and input schemas that
 `tools/list` advertises over MCP. Path parameters are required strings whose
 description names the segment index, the templating rule and the observed
-values; query parameter names are optional strings; write methods accept an
+values (sampled within the list budget above; the manifest keeps them all);
+query parameter names are optional strings; write methods accept an
 optional `body` object described by the recorded top-level key types. Each
 input keeps its own argument: a query name equal to a path parameter's name is
 advertised as `query_<name>`, and the write body as `request_body` when a query
diff --git a/scripts/verify-package-setup-plan.d.mts b/scripts/verify-package-setup-plan.d.mts
new file mode 100644
index 0000000000..08fe24aed8
--- /dev/null
+++ b/scripts/verify-package-setup-plan.d.mts
@@ -0,0 +1,8 @@
+/** Preserve an unexpected JSON result while describing the failed plan check. */
+export function setupPlanFailureMessage(options: {
+  readonly planned: unknown;
+  readonly plannedExecution: { readonly status: number | null };
+  readonly plannedClaudeConfig: string;
+  readonly plannedCodexConfig: string;
+  readonly plannedCursorConfig: string;
+}): string;
diff --git a/scripts/verify-package-setup-plan.mjs b/scripts/verify-package-setup-plan.mjs
new file mode 100644
index 0000000000..4734607367
--- /dev/null
+++ b/scripts/verify-package-setup-plan.mjs
@@ -0,0 +1,23 @@
+/** Describe a failed package setup-plan check without masking its result shape. */
+export const setupPlanFailureMessage = ({
+  planned,
+  plannedExecution,
+  plannedClaudeConfig,
+  plannedCodexConfig,
+  plannedCursorConfig,
+}) => {
+  const actionKinds = (actions) =>
+    Array.isArray(actions)
+      ? actions.map((action) => action?.kind ?? action)
+      : actions;
+  return `packaged setup plan was not read-only: ${JSON.stringify({
+    status: planned?.status,
+    exitCode: plannedExecution.status,
+    plannedKinds: actionKinds(planned?.plannedActions),
+    appliedKinds: actionKinds(planned?.appliedActions),
+    result: planned,
+    claudeConfig: plannedClaudeConfig,
+    codexConfig: plannedCodexConfig,
+    cursorConfig: plannedCursorConfig,
+  })}`;
+};
diff --git a/scripts/verify-package-setup.mjs b/scripts/verify-package-setup.mjs
index ad23548cb3..e44c4f5c88 100644
--- a/scripts/verify-package-setup.mjs
+++ b/scripts/verify-package-setup.mjs
@@ -21,6 +21,7 @@ import {
 } from "./lib/verify-package-core.mjs";
 import { parse as parseJsonc } from "jsonc-parser";
 import { skillReferenceIssues } from "./lib/docs-facts.mjs";
+import { setupPlanFailureMessage } from "./verify-package-setup-plan.mjs";
 
 export const terminalModesRestored = (termios) => {
   if (typeof termios !== "string") return false;
@@ -250,23 +251,37 @@ const verifySetupPlan = async ({
   );
   const planned = json(plannedExecution.stdout);
   if (supportedSetupHost) {
+    const plannedActions = Array.isArray(planned?.plannedActions)
+      ? planned.plannedActions
+      : undefined;
+    const appliedActions = Array.isArray(planned?.appliedActions)
+      ? planned.appliedActions
+      : undefined;
     const plannedClaudeConfig = await readFile(claudeConfig, "utf8");
     const plannedCodexConfig = await readFile(codexTarget, "utf8");
     const plannedCursorConfig = await readFile(cursorConfig, "utf8");
     const plannedOpenCodeConfig = await readFile(opencodeConfig, "utf8");
     if (
-      planned.status !== "planned" ||
+      planned?.status !== "planned" ||
       plannedExecution.status !== 0 ||
-      planned.appliedActions.length !== 0 ||
-      !planned.plannedActions.some(({ kind }) => kind === "configure_client") ||
-      !planned.plannedActions.some(({ kind }) => kind === "install_skill") ||
+      plannedActions === undefined ||
+      appliedActions === undefined ||
+      appliedActions.length !== 0 ||
+      !plannedActions.some((action) => action?.kind === "configure_client") ||
+      !plannedActions.some((action) => action?.kind === "install_skill") ||
       plannedClaudeConfig !== '{"existing":true}\n' ||
       plannedCodexConfig !== CODEX_ORIGINAL ||
       plannedCursorConfig !== '{"existing":true}\n' ||
       plannedOpenCodeConfig !== opencodeOriginal
     )
       throw new Error(
-        `packaged setup plan was not read-only: ${JSON.stringify({ status: planned.status, exitCode: plannedExecution.status, plannedKinds: planned.plannedActions.map(({ kind }) => kind), appliedKinds: planned.appliedActions.map(({ kind }) => kind), claudeConfig: plannedClaudeConfig, codexConfig: plannedCodexConfig, cursorConfig: plannedCursorConfig })}`,
+        setupPlanFailureMessage({
+          planned,
+          plannedExecution,
+          plannedClaudeConfig,
+          plannedCodexConfig,
+          plannedCursorConfig,
+        }),
       );
   }
   return { planned };
diff --git a/scripts/verify/recorded-crash/trace-ownership.d.mts b/scripts/verify/recorded-crash/trace-ownership.d.mts
new file mode 100644
index 0000000000..0daeba3737
--- /dev/null
+++ b/scripts/verify/recorded-crash/trace-ownership.d.mts
@@ -0,0 +1,6 @@
+/** Assert the documented procfs allowance over strace -ff process/thread files. */
+export function assertHistoricalPidReadsAreOwnershipOnly(options: {
+  readonly traces: readonly { readonly pid: number; readonly text: string }[];
+  readonly sentinelPid: number;
+  readonly psExecutables: ReadonlySet<string>;
+}): string[];
diff --git a/scripts/verify/recorded-crash/trace-ownership.mjs b/scripts/verify/recorded-crash/trace-ownership.mjs
new file mode 100644
index 0000000000..0267dcdaa8
--- /dev/null
+++ b/scripts/verify/recorded-crash/trace-ownership.mjs
@@ -0,0 +1,127 @@
+import assert from "node:assert/strict";
+
+const ownershipPsArguments =
+  '["ps", "-axo", "pid=,ppid=,pgid=,uid=,stat=,command="]';
+
+/**
+ * Allow only the procfs paths used by the process-ownership scan: ps may
+ * inspect its process-table fields, and its caller's thread group may read
+ * native identity and UID records. With strace -ff, libuv worker threads get
+ * separate files; follow CLONE_THREAD edges, never ordinary child-process
+ * edges. strace cannot distinguish the purpose of a stat/status read inside
+ * the same Node thread group, so this is deliberately limited to those two
+ * files; provider Python/GDB children remain outside the permit.
+ */
+export const assertHistoricalPidReadsAreOwnershipOnly = ({
+  traces,
+  sentinelPid,
+  psExecutables,
+}) => {
+  const processGroups = new Map();
+  const findGroup = (pid) => {
+    const parent = processGroups.get(pid);
+    if (parent === undefined) {
+      processGroups.set(pid, pid);
+      return pid;
+    }
+    if (parent === pid) return pid;
+    const root = findGroup(parent);
+    processGroups.set(pid, root);
+    return root;
+  };
+  const joinThreadGroup = (left, right) => {
+    const leftRoot = findGroup(left);
+    const rightRoot = findGroup(right);
+    if (leftRoot !== rightRoot) processGroups.set(rightRoot, leftRoot);
+  };
+
+  const cloneEvents = [];
+  for (const trace of traces) {
+    let unfinished;
+    for (const rawLine of trace.text.split("\n")) {
+      const line = rawLine.trimStart();
+      const start = /^(clone3?|fork|vfork)\((.*)<unfinished \.\.\.>$/u.exec(
+        line,
+      );
+      if (start !== null) {
+        unfinished = { name: start[1], text: start[2] };
+        continue;
+      }
+      const resumed = /^<\.\.\. (clone3?|fork|vfork) resumed>(.*)$/u.exec(line);
+      if (resumed !== null && resumed[1] === unfinished?.name) {
+        cloneEvents.push({
+          parentPid: trace.pid,
+          text: `${unfinished.text}${resumed[2]}`,
+        });
+        unfinished = undefined;
+        continue;
+      }
+      const complete =
+        /^(clone3?|fork|vfork)\((.*\)) = (\d+)(?:<[^>]*>)?$/u.exec(line);
+      if (complete !== null)
+        cloneEvents.push({
+          parentPid: trace.pid,
+          childPid: Number(complete[3]),
+          text: complete[2],
+        });
+    }
+  }
+
+  for (const event of cloneEvents) {
+    const childPid =
+      event.childPid ?? /\) = (\d+)(?:<[^>]*>)?$/u.exec(event.text)?.[1];
+    if (childPid === undefined) continue;
+    event.childPid = Number(childPid);
+    if (/\bCLONE_THREAD\b/u.test(event.text))
+      joinThreadGroup(event.parentPid, event.childPid);
+  }
+
+  const psPids = new Set();
+  for (const trace of traces) {
+    const successfulPsExec = trace.text.split("\n").some((line) => {
+      const executable = /^execve\("([^"]+)"/u.exec(line)?.[1];
+      return (
+        executable !== undefined &&
+        psExecutables.has(executable) &&
+        line.includes(ownershipPsArguments) &&
+        line.endsWith(" = 0")
+      );
+    });
+    if (successfulPsExec) psPids.add(trace.pid);
+  }
+
+  const psParentGroups = new Set(
+    cloneEvents
+      .filter(({ childPid }) => childPid !== undefined && psPids.has(childPid))
+      .map(({ parentPid }) => findGroup(parentPid)),
+  );
+
+  const ownershipReads = [];
+  const pidPrefix = `/proc/${sentinelPid}/`;
+  for (const trace of traces) {
+    const isPsProcess = psPids.has(trace.pid);
+    const isOwnershipProcessThread = psParentGroups.has(findGroup(trace.pid));
+    const pidReads = trace.text
+      .split("\n")
+      .filter((line) => line.includes(pidPrefix));
+    for (const line of pidReads) {
+      const psAllowedPath = new RegExp(
+        `/proc/${sentinelPid}/(?:stat|status|cmdline|wchan|environ)"`,
+        "u",
+      ).test(line);
+      const ownershipThreadPath = new RegExp(
+        `/proc/${sentinelPid}/(?:stat|status)"`,
+        "u",
+      ).test(line);
+      const psRead = isPsProcess && psAllowedPath;
+      const ownershipThreadRead =
+        isOwnershipProcessThread && ownershipThreadPath;
+      assert.ok(
+        psRead || ownershipThreadRead,
+        `Historical PID caused a provider lookup in trace.${trace.pid}: ${line}`,
+      );
+      ownershipReads.push(line);
+    }
+  }
+  return ownershipReads;
+};
diff --git a/scripts/verify/recorded-crash/trace.mjs b/scripts/verify/recorded-crash/trace.mjs
index 7cf5835087..44ef4f9632 100644
--- a/scripts/verify/recorded-crash/trace.mjs
+++ b/scripts/verify/recorded-crash/trace.mjs
@@ -3,6 +3,7 @@ import { readdir, readFile, realpath } from "node:fs/promises";
 import { fileURLToPath } from "node:url";
 import { isAbsolute, join, resolve } from "node:path";
 import { runOwnedCommand } from "../../../dist/process/OwnedCommand.js";
+import { assertHistoricalPidReadsAreOwnershipOnly } from "./trace-ownership.mjs";
 
 /** Check attempted syscalls, including failed attempts, on a recorded PID that collides with an owned live sentinel. */
 export async function verifyCoreInspectionTrace({
@@ -68,11 +69,22 @@ export async function verifyCoreInspectionTrace({
       { timeoutMs: 90_000, diagnosticBytes: 1024 * 1024 },
     );
     const executions = [];
-    const ownershipReads = [];
     let gdbObserved = false;
-    for (const file of await readdir(root)) {
-      if (!file.startsWith(`inspection-${mode}.trace.`)) continue;
-      const text = await readFile(join(root, file), "utf8");
+    const traces = await Promise.all(
+      (await readdir(root))
+        .filter((file) => file.startsWith(`inspection-${mode}.trace.`))
+        .map(async (file) => ({
+          file,
+          pid: Number(file.slice(`inspection-${mode}.trace.`.length)),
+          text: await readFile(join(root, file), "utf8"),
+        })),
+    );
+    const ownershipReads = assertHistoricalPidReadsAreOwnershipOnly({
+      traces,
+      sentinelPid: sentinel.pid,
+      psExecutables: psPaths,
+    });
+    for (const { file, text } of traces) {
       // Keep the source executable present: GDB 16 otherwise silently hides a
       // core-only violation when its automatic executable lookup finds nothing.
       const recordedExecutable = JSON.stringify(join(root, "fixture-program"));
@@ -80,36 +92,6 @@ export async function verifyCoreInspectionTrace({
         !text.split("\n").some((line) => line.includes(recordedExecutable)),
         `Inspection attempted access to the recorded executable: ${file}`,
       );
-      const ownershipTrace = text
-        .split("\n")
-        .some(
-          (line) =>
-            /^execve\("\/(?:usr\/)?bin\/ps",/u.test(line) &&
-            line.includes(
-              '["ps", "-axo", "pid=,ppid=,pgid=,uid=,stat=,command="]',
-            ) &&
-            line.endsWith(" = 0"),
-        );
-      const pidReads = text
-        .split("\n")
-        .filter((line) => line.includes(`/proc/${sentinel.pid}/`));
-      if (ownershipTrace) {
-        for (const line of pidReads) {
-          assert.ok(
-            new RegExp(
-              `/proc/${sentinel.pid}/(?:stat|status|cmdline|wchan|environ)"`,
-              "u",
-            ).test(line),
-            `Unexpected ownership observation of the sentinel: ${line}`,
-          );
-          ownershipReads.push(line);
-        }
-      } else
-        assert.deepEqual(
-          pidReads,
-          [],
-          `Historical PID caused a provider lookup in ${file}: ${pidReads.join("\n")}`,
-        );
       assert.ok(
         !/\bptrace\(/u.test(text),
         `Inspection attempted ptrace: ${file}`,
diff --git a/src/browser/history/HarCapture.ts b/src/browser/history/HarCapture.ts
index 9e164e92d9..ec55644d0e 100644
--- a/src/browser/history/HarCapture.ts
+++ b/src/browser/history/HarCapture.ts
@@ -2,7 +2,7 @@ import { createHash } from "node:crypto";
 import { LosslessNumber } from "lossless-json";
 import { parseCaptureJson } from "./CaptureJson.js";
 import type { JsonValue } from "../../domain/jsonValue.js";
-import { CANONICAL_BASE64_PATTERN } from "../../domain/stringPatterns.js";
+import { isCanonicalBase64 } from "../../domain/stringPatterns.js";
 import {
   WEB_NETWORK_CAPTURE_LIMITS,
   type WebNetworkCapture,
@@ -265,7 +265,7 @@ const integerLexeme = (literal: string): boolean => {
 
 const decodeHarBase64 = (value: string, pointer: string): Buffer => {
   const compact = value.replace(/[\t\n\r ]/g, "");
-  if (compact.length % 4 !== 0 || !CANONICAL_BASE64_PATTERN.test(compact))
+  if (!isCanonicalBase64(compact))
     throw new CaptureFormatError(
       "format",
       "HAR content declares base64 but its text is not valid canonical base64 (ASCII whitespace is allowed).",
diff --git a/src/domain/go/goBinary.ts b/src/domain/go/goBinary.ts
index 8714159c38..550d7a8348 100644
--- a/src/domain/go/goBinary.ts
+++ b/src/domain/go/goBinary.ts
@@ -1,7 +1,7 @@
 import { z } from "zod";
 import { digestSchema } from "../digests.js";
 import { localPathStringSchema } from "../localPath.js";
-import { CANONICAL_BASE64_PATTERN } from "../stringPatterns.js";
+import { canonicalBase64Schema } from "../stringPatterns.js";
 
 const sourceRangeSchema = z.strictObject({
   offset: z.number().int().nonnegative(),
@@ -25,9 +25,7 @@ export const goModuleMetadataSchema = z.strictObject({
   dependencies: z.array(goModuleSchema),
   settings: z.array(z.strictObject({ key: z.string(), value: z.string() })),
   unparsed_lines: z.array(z.string()),
-  unparsed_line_bytes_base64: z.array(
-    z.string().regex(CANONICAL_BASE64_PATTERN),
-  ),
+  unparsed_line_bytes_base64: z.array(canonicalBase64Schema),
   complete: z.boolean(),
 });
 
@@ -43,9 +41,9 @@ export const goBuildInfoSchema = z.strictObject({
   header_offset: z.number().int().nonnegative(),
   encoding: z.enum(["inline", "pointer"]),
   go_version: z.string().nullable(),
-  go_version_bytes_base64: z.string().regex(CANONICAL_BASE64_PATTERN),
+  go_version_bytes_base64: canonicalBase64Schema,
   module_text: z.string().nullable(),
-  module_bytes_base64: z.string().regex(CANONICAL_BASE64_PATTERN),
+  module_bytes_base64: canonicalBase64Schema,
   version_location: sourceRangeSchema,
   module_location: sourceRangeSchema,
   module: goModuleMetadataSchema,
diff --git a/src/domain/native/binaryLayout.ts b/src/domain/native/binaryLayout.ts
index cc37376dd9..c1a694cc2d 100644
--- a/src/domain/native/binaryLayout.ts
+++ b/src/domain/native/binaryLayout.ts
@@ -2,13 +2,13 @@ import { z } from "zod";
 import { canBorrowParsedJsonSnapshot } from "../immutableJson.js";
 
 import { localPathStringSchema } from "../localPath.js";
-import { CANONICAL_BASE64_PATTERN } from "../stringPatterns.js";
+import { canonicalBase64Schema } from "../stringPatterns.js";
 
 const unsignedHex = z.string().regex(/^0x(?:0|[1-9a-f][0-9a-f]{0,15})$/);
 const index = z.number().int().nonnegative();
 const scalar = z.union([z.string(), z.number().int()]);
 const range = z.strictObject({ offset: unsignedHex, bytes: unsignedHex });
-const canonicalBase64 = z.string().regex(CANONICAL_BASE64_PATTERN);
+const canonicalBase64 = canonicalBase64Schema;
 const name = z.strictObject({
   display: z.string(),
   bytes_base64: canonicalBase64.nullable(),
diff --git a/src/domain/native/recordedCrash.ts b/src/domain/native/recordedCrash.ts
index 8bd04cac14..0163a85329 100644
--- a/src/domain/native/recordedCrash.ts
+++ b/src/domain/native/recordedCrash.ts
@@ -2,13 +2,13 @@ import { z } from "zod";
 
 import type { BinaryArchitecture } from "../binaryTargetTypes.js";
 import { localPathStringSchema } from "../localPath.js";
-import { CANONICAL_BASE64_PATTERN } from "../stringPatterns.js";
+import { canonicalBase64Schema } from "../stringPatterns.js";
 import { recordedNoteCoverageIssues } from "./recordedCrashNoteCoverage.js";
 
 const hex = z.string().regex(/^0x(?:0|[1-9a-f][0-9a-f]{0,15})$/);
 const index = z.number().int().nonnegative();
 const signed32 = z.number().int().min(-2147483648).max(2147483647);
-const base64 = z.string().regex(CANONICAL_BASE64_PATTERN);
+const base64 = canonicalBase64Schema;
 const range = z.strictObject({ offset: hex, bytes: hex });
 const diagnostics = z.strictObject({
   stdout: z.string(),
diff --git a/src/domain/paddedBase64.ts b/src/domain/paddedBase64.ts
index 395bdf5b8e..b4402f6b5e 100644
--- a/src/domain/paddedBase64.ts
+++ b/src/domain/paddedBase64.ts
@@ -1,9 +1,8 @@
-import { PADDED_BASE64_PATTERN } from "./stringPatterns.js";
+import { isPaddedBase64 } from "./stringPatterns.js";
 
 /** Validate padded syntax without imposing canonical zero pad bits. */
 export const paddedBase64ByteLength = (value: string): number | undefined => {
-  if (value.length % 4 !== 0 || !PADDED_BASE64_PATTERN.test(value))
-    return undefined;
+  if (!isPaddedBase64(value)) return undefined;
   const padding = value.endsWith("==") ? 2 : value.endsWith("=") ? 1 : 0;
   return (value.length / 4) * 3 - padding;
 };
diff --git a/src/domain/stringPatterns.test.ts b/src/domain/stringPatterns.test.ts
index 7537742bd3..4410ad7b95 100644
--- a/src/domain/stringPatterns.test.ts
+++ b/src/domain/stringPatterns.test.ts
@@ -1,10 +1,16 @@
 import { expect, it } from "vitest";
+import { z } from "zod";
 
 import {
-  CANONICAL_BASE64_PATTERN,
+  BASE64_QUARTET_LENGTH_PATTERN,
+  INVALID_BASE64_CHARACTER_PATTERN,
+  INVALID_BASE64_PADDING_PATTERN,
+  INVALID_CANONICAL_BASE64_PAD_BITS_PATTERN,
   IDENTIFIER_PATTERN,
-  PADDED_BASE64_PATTERN,
   STABLE_IDENTIFIER_PATTERN,
+  canonicalBase64Schema,
+  isCanonicalBase64,
+  isPaddedBase64,
 } from "./stringPatterns.js";
 
 it("preserves identifier grammars under Unicode and Unicode-set compilation", () => {
@@ -43,7 +49,7 @@ it("preserves identifier grammars under Unicode and Unicode-set compilation", ()
   }
 });
 
-it("preserves canonical base64 padding and pad-bit validation", () => {
+it("preserves canonical and permissive padded base64 validation", () => {
   const previous =
     /^(?:[A-Za-z0-9+/]{4})*(?:[A-Za-z0-9+/][AQgw]==|[A-Za-z0-9+/]{2}[AEIMQUYcgkosw048]=)?$/;
   const samples = [
@@ -71,28 +77,62 @@ it("preserves canonical base64 padding and pad-bit validation", () => {
   for (const first of alphabet)
     for (const second of alphabet)
       samples.push(`${first}${second}==`, `A${first}${second}=`);
-  for (const flag of ["u", "v"]) {
-    const projected = new RegExp(CANONICAL_BASE64_PATTERN.source, flag);
-    for (const sample of samples)
-      expect(projected.test(sample), JSON.stringify({ flag, sample })).toBe(
-        previous.test(sample),
-      );
+  for (const sample of samples) {
+    expect(isCanonicalBase64(sample), JSON.stringify({ sample })).toBe(
+      previous.test(sample),
+    );
+    expect(isPaddedBase64(sample), JSON.stringify({ sample })).toBe(
+      sample.length % 4 === 0 && /^[A-Za-z0-9+/]*(?:==|=)?$/.test(sample),
+    );
   }
 });
 
-it("validates large canonical base64 under JSON Schema Unicode modes", () => {
-  // Near the 32 MiB capture input budget: a quartet expansion alone still
-  // overflows at this size, especially in Unicode-set client validators.
+it("advertises every portable base64 constraint and keeps large inputs stack-safe", () => {
+  const jsonSchema = z.toJSONSchema(canonicalBase64Schema, {
+    target: "draft-2020-12",
+  });
+  expect(jsonSchema).toMatchObject({
+    allOf: expect.arrayContaining([
+      { pattern: BASE64_QUARTET_LENGTH_PATTERN.source },
+      { not: { pattern: INVALID_BASE64_CHARACTER_PATTERN.source } },
+      { not: { pattern: INVALID_BASE64_PADDING_PATTERN.source } },
+      { not: { pattern: INVALID_CANONICAL_BASE64_PAD_BITS_PATTERN.source } },
+    ]),
+  });
+
   const body = Buffer.alloc(24 * 1024 * 1024 - 3, 0x81);
   const encoded = body.toString("base64");
   for (const flag of ["", "u", "v"]) {
-    const pattern = new RegExp(CANONICAL_BASE64_PATTERN.source, flag);
-    expect(pattern.test(encoded), flag).toBe(true);
-    expect(pattern.test(`${encoded.slice(0, -1)}!`), flag).toBe(false);
-    expect(pattern.test(`${encoded.slice(0, -3)}R==`), flag).toBe(false);
-    expect(pattern.test(`${encoded}A`), flag).toBe(false);
-    const padded = new RegExp(PADDED_BASE64_PATTERN.source, flag);
-    expect(padded.test(encoded), flag).toBe(true);
-    expect(padded.test(`${encoded.slice(0, -1)}!`), flag).toBe(false);
+    expect(
+      new RegExp(BASE64_QUARTET_LENGTH_PATTERN.source, flag).test(encoded),
+      flag,
+    ).toBe(true);
+    expect(
+      new RegExp(INVALID_BASE64_CHARACTER_PATTERN.source, flag).test(encoded),
+      flag,
+    ).toBe(false);
+    expect(
+      new RegExp(INVALID_BASE64_PADDING_PATTERN.source, flag).test(encoded),
+      flag,
+    ).toBe(false);
+    expect(
+      new RegExp(INVALID_CANONICAL_BASE64_PAD_BITS_PATTERN.source, flag).test(
+        encoded,
+      ),
+      flag,
+    ).toBe(false);
+    expect(
+      new RegExp(INVALID_BASE64_CHARACTER_PATTERN.source, flag).test(
+        `${encoded.slice(0, -1)}!`,
+      ),
+      flag,
+    ).toBe(true);
+    expect(
+      new RegExp(INVALID_CANONICAL_BASE64_PAD_BITS_PATTERN.source, flag).test(
+        `${encoded.slice(0, -3)}R==`,
+      ),
+      flag,
+    ).toBe(true);
   }
+  expect(isCanonicalBase64(encoded)).toBe(true);
 });
diff --git a/src/domain/stringPatterns.ts b/src/domain/stringPatterns.ts
index ab8994f17f..718cc1d1d4 100644
--- a/src/domain/stringPatterns.ts
+++ b/src/domain/stringPatterns.ts
@@ -1,20 +1,44 @@
+import { z } from "zod";
+
 /** Portable ASCII identifier starting with a letter. */
 export const IDENTIFIER_PATTERN = /^[A-Za-z][A-Za-z0-9._\x2d]*$/u;
 
 /** Stable evidence identifier, also admitting namespace and path separators. */
 export const STABLE_IDENTIFIER_PATTERN = /^[A-Za-z][A-Za-z0-9._:\x2f\x2d]*$/u;
 
-// Repeated alphabet quartets exhaust V8's regexp stack on large bodies,
-// including under JSON Schema's Unicode-set mode. Check alphabet and terminal
-// padding separately, leaving an unconstrained fixed-width loop for length.
-const PADDED_BASE64_PREFIX = String.raw`^(?!.*[^A-Za-z0-9+\x2f=])(?!.*=[^=])(?!.*===)`;
+// These rules are separate JSON Schema constraints. A single RE2-compatible
+// regex for alphabet and quartet validity requires a repeated alphabet group;
+// V8's Unicode-set engine overflows its regexp stack on that group near the
+// provider's 32 MiB encoded-input budget. Wildcard quartets and literal bad
+// token probes stay stack-safe at that size and compose exactly with `allOf`.
+export const BASE64_QUARTET_LENGTH_PATTERN = /^(?:....)*$/;
+export const INVALID_BASE64_CHARACTER_PATTERN = /[^A-Za-z0-9+\x2f=]/;
+export const INVALID_BASE64_PADDING_PATTERN = /(?:=[^=]|===)/;
+export const INVALID_CANONICAL_BASE64_PAD_BITS_PATTERN =
+  /(?:[^AQgw]==$|[BCDFGHJKLNOPRSTVWXZabdefhijlmnpqrtuvxyz1235679+\x2f]=$)/;
 
-/** Padded base64 syntax, allowing nonzero pad bits and the empty encoding. */
-export const PADDED_BASE64_PATTERN = new RegExp(
-  `${PADDED_BASE64_PREFIX}(?:....)*$`,
-);
+export const isPaddedBase64 = (value: string): boolean =>
+  value.length % 4 === 0 &&
+  !INVALID_BASE64_CHARACTER_PATTERN.test(value) &&
+  !INVALID_BASE64_PADDING_PATTERN.test(value);
 
-/** Canonical padded base64, including zero pad bits and the empty encoding. */
-export const CANONICAL_BASE64_PATTERN = new RegExp(
-  `${PADDED_BASE64_PREFIX}(?!.*[^AQgw]==$)(?!.*[^AEIMQUYcgkosw048=]=$)(?:....)*$`,
-);
+export const isCanonicalBase64 = (value: string): boolean =>
+  isPaddedBase64(value) &&
+  !INVALID_CANONICAL_BASE64_PAD_BITS_PATTERN.test(value);
+
+const paddedBase64SchemaRules = [
+  { pattern: BASE64_QUARTET_LENGTH_PATTERN.source },
+  { not: { pattern: INVALID_BASE64_CHARACTER_PATTERN.source } },
+  { not: { pattern: INVALID_BASE64_PADDING_PATTERN.source } },
+];
+
+/** Canonical padded base64 with zero pad bits, including the empty encoding. */
+export const canonicalBase64Schema = z
+  .string()
+  .refine(isCanonicalBase64, "Expected canonical padded base64")
+  .meta({
+    allOf: [
+      ...paddedBase64SchemaRules,
+      { not: { pattern: INVALID_CANONICAL_BASE64_PAD_BITS_PATTERN.source } },
+    ],
+  });
diff --git a/src/process/LinuxProcessStatus.test.ts b/src/process/LinuxProcessStatus.test.ts
new file mode 100644
index 0000000000..46f7688447
--- /dev/null
+++ b/src/process/LinuxProcessStatus.test.ts
@@ -0,0 +1,21 @@
+import { expect, it } from "vitest";
+
+import { parseLinuxProcessEffectiveUid } from "./LinuxProcessStatus.js";
+
+it("parses the effective UID from the single native status Uid row", () => {
+  expect(
+    parseLinuxProcessEffectiveUid(
+      "Name:\tworker\nUid:\t1000\t1001\t1002\t1003\nGid:\t20\t20\t20\t20\n",
+    ),
+  ).toBe(1001);
+});
+
+it.each([
+  "Name:\tworker\n",
+  "Uid:\t1000\t1001\t1002\n",
+  "Uid:\t1000\t1001\t1002\t1003\nUid:\t1000\t1001\t1002\t1003\n",
+  "Uid:\t1000\t-1\t1002\t1003\n",
+  "Uid:\t1000\t9007199254740992\t1002\t1003\n",
+])("does not infer an effective UID from malformed status: %s", (status) => {
+  expect(parseLinuxProcessEffectiveUid(status)).toBeUndefined();
+});
diff --git a/src/process/LinuxProcessStatus.ts b/src/process/LinuxProcessStatus.ts
new file mode 100644
index 0000000000..60d8f2809e
--- /dev/null
+++ b/src/process/LinuxProcessStatus.ts
@@ -0,0 +1,19 @@
+/** Effective UID parsed from one Linux `/proc/<pid>/status` record. */
+export const parseLinuxProcessEffectiveUid = (
+  value: string,
+): number | undefined => {
+  let effectiveUid: number | undefined;
+  for (const line of value.split("\n")) {
+    if (!line.startsWith("Uid:")) continue;
+    if (effectiveUid !== undefined) return undefined;
+    const match = /^Uid:\s+([0-9]+)\s+([0-9]+)\s+([0-9]+)\s+([0-9]+)\s*$/u.exec(
+      line,
+    );
+    if (match === null) return undefined;
+    const values = match.slice(1).map(Number);
+    if (values.some((uid) => !Number.isSafeInteger(uid) || uid < 0))
+      return undefined;
+    effectiveUid = values[1];
+  }
+  return effectiveUid;
+};
diff --git a/src/process/ProcessOwnership.identity.test.ts b/src/process/ProcessOwnership.identity.test.ts
index 1d518fda2c..5b5c69f988 100644
--- a/src/process/ProcessOwnership.identity.test.ts
+++ b/src/process/ProcessOwnership.identity.test.ts
@@ -32,7 +32,11 @@ describe("Linux process start identities", () => {
       state: "S",
       command: process.execPath,
     } satisfies ProcessTableEntry;
-    const identities = await host.processIdentities?.([observedProcess]);
+    const identities = await host.processIdentities?.(
+      [observedProcess],
+      undefined,
+      new Set([observedProcess.pid]),
+    );
     expect(identities?.get(observedProcess.pid)).toMatchObject({
       state: "readable",
       identity: expect.stringMatching(/^linux-starttime:\d+$/u),
@@ -43,8 +47,9 @@ describe("Linux process start identities", () => {
         processGroupId: expect.any(Number),
       },
     });
-    expect(identities?.get(observedProcess.pid)).not.toHaveProperty(
+    expect(identities?.get(observedProcess.pid)).toHaveProperty(
       "effectiveUid",
+      process.geteuid!(),
     );
     const baseline = await host.captureBaseline?.();
     expect(baseline).toContainEqual({
@@ -110,9 +115,11 @@ it("validates and cleans an exact-token owner without a capture baseline", async
   expect(signalGroup).toHaveBeenCalledWith(process.processGroupId, "SIGKILL");
 });
 
-it.skipIf(typeof process.getuid !== "function")(
-  "uses a same-generation native UID instead of the process-table UID for unreadable tokens",
-  async () => {
+it
+  .skipIf(typeof process.getuid !== "function")
+  .each(["EINVAL", "EACCES: permission denied"])(
+  "uses a same-generation native UID instead of the process-table UID for unreadable tokens: %s",
+  async (diagnostic) => {
     const callerUid = process.getuid!();
     const foreignUid = callerUid === 0 ? 1 : 0;
     const verify = async (rowUid: number, effectiveUid: number) => {
@@ -132,7 +139,7 @@ it.skipIf(typeof process.getuid !== "function")(
         runTokens: () =>
           Promise.resolve(
             new Map([
-              [906, { state: "unavailable", reason: "EINVAL" } as const],
+              [906, { state: "unavailable", reason: diagnostic } as const],
             ]),
           ),
         processIdentities: (entries) =>
@@ -161,7 +168,7 @@ it.skipIf(typeof process.getuid !== "function")(
     });
     await expect(verify(callerUid, foreignUid)).resolves.toMatchObject({
       cleaned: true,
-      unverified: [{ pid: 906, diagnostic: "EINVAL" }],
+      unverified: [{ pid: 906, diagnostic }],
     });
   },
 );
diff --git a/src/process/ProcessOwnership.procIdentity.test.ts b/src/process/ProcessOwnership.procIdentity.test.ts
index 6b2eaa3eb6..fff53db724 100644
--- a/src/process/ProcessOwnership.procIdentity.test.ts
+++ b/src/process/ProcessOwnership.procIdentity.test.ts
@@ -9,8 +9,14 @@ vi.mock("node:fs/promises", async (importOriginal) => {
   return { ...original, readFile: filesystem.readFile };
 });
 
-import { createSystemProcessOwnershipHost } from "./ProcessOwnershipObservation.js";
-import type { ProcessTableEntry } from "./ProcessOwnership.js";
+import {
+  createSystemProcessOwnershipHost,
+  readProcessOwnershipFacts,
+} from "./ProcessOwnershipObservation.js";
+import type {
+  ProcessOwnershipHost,
+  ProcessTableEntry,
+} from "./ProcessOwnership.js";
 
 const entry: ProcessTableEntry = {
   pid: 42,
@@ -23,6 +29,144 @@ const entry: ProcessTableEntry = {
 const filesystemError = (code: string): NodeJS.ErrnoException =>
   Object.assign(new Error(code), { code });
 
+const procStat = (
+  startTime: number,
+  parentPid = 1,
+  processGroupId = 42,
+  pid = 42,
+) => {
+  const fields = ["S", String(parentPid), String(processGroupId), "42"];
+  while (fields.length < 19) fields.push("0");
+  fields.push(String(startTime));
+  return `${String(pid)} (fixture) ${fields.join(" ")}`;
+};
+
+it("binds Linux effective UID to the same native process generation", async () => {
+  const host = createSystemProcessOwnershipHost("linux", {});
+  filesystem.readFile
+    .mockResolvedValueOnce(procStat(100, 10, 42))
+    .mockResolvedValueOnce("Name:\tfixture\nUid:\t1000\t1001\t1002\t1003\n")
+    .mockResolvedValueOnce(procStat(100, 11, 43));
+
+  await expect(
+    host.processIdentities?.([entry], undefined, new Set([entry.pid])),
+  ).resolves.toEqual(
+    new Map([
+      [
+        42,
+        {
+          state: "readable",
+          identity: "linux-starttime:100",
+          effectiveUid: 1001,
+          lifecycle: { state: "observed", lifecycle: "non-zombie" },
+          relation: {
+            state: "observed",
+            parentPid: 11,
+            processGroupId: 43,
+          },
+        },
+      ],
+    ]),
+  );
+  expect(filesystem.readFile.mock.calls.map(([path]) => path)).toEqual([
+    "/proc/42/stat",
+    "/proc/42/status",
+    "/proc/42/stat",
+  ]);
+});
+
+it("keeps native identity when status UID is unavailable", async () => {
+  const host = createSystemProcessOwnershipHost("linux", {});
+  filesystem.readFile
+    .mockResolvedValueOnce(procStat(100))
+    .mockRejectedValueOnce(filesystemError("EACCES"));
+
+  await expect(
+    host.processIdentities?.([entry], undefined, new Set([entry.pid])),
+  ).resolves.toEqual(
+    new Map([
+      [
+        42,
+        {
+          state: "readable",
+          identity: "linux-starttime:100",
+          lifecycle: { state: "observed", lifecycle: "non-zombie" },
+          relation: {
+            state: "observed",
+            parentPid: 1,
+            processGroupId: 42,
+          },
+        },
+      ],
+    ]),
+  );
+  expect(filesystem.readFile).toHaveBeenCalledTimes(2);
+});
+
+it("does not attach a UID when the process generation changes around status", async () => {
+  const host = createSystemProcessOwnershipHost("linux", {});
+  filesystem.readFile
+    .mockResolvedValueOnce(procStat(100))
+    .mockResolvedValueOnce("Uid:\t1000\t1001\t1002\t1003\n")
+    .mockResolvedValueOnce(procStat(101));
+
+  await expect(
+    host.processIdentities?.([entry], undefined, new Set([entry.pid])),
+  ).resolves.toEqual(
+    new Map([
+      [
+        42,
+        {
+          state: "unavailable",
+          reason: "process_identity_changed_during_uid_observation",
+        },
+      ],
+    ]),
+  );
+});
+
+it("reads Linux effective UID only for token-unavailable rows", async () => {
+  const rows = [entry, { ...entry, pid: 43, processGroupId: 43 }];
+  const statReads = new Map<number, number>();
+  const uidStatusPids: number[] = [];
+  filesystem.readFile.mockImplementation(async (path) => {
+    const match = /^\/proc\/(\d+)\/(stat|status)$/u.exec(String(path));
+    if (match === null) throw new Error(`unexpected path: ${String(path)}`);
+    const pid = Number(match[1]);
+    if (match[2] === "status") {
+      uidStatusPids.push(pid);
+      return "Uid:\t1000\t1001\t1002\t1003\n";
+    }
+    const reads = (statReads.get(pid) ?? 0) + 1;
+    statReads.set(pid, reads);
+    return procStat(100, 1, pid, pid);
+  });
+  const systemHost = createSystemProcessOwnershipHost("linux", {});
+  const host: ProcessOwnershipHost = {
+    ...systemHost,
+    runTokens: async () =>
+      new Map([
+        [entry.pid, { state: "unavailable", reason: "EACCES" }],
+        [43, { state: "readable", runId: undefined }],
+      ]),
+  };
+
+  const facts = await readProcessOwnershipFacts(rows, host);
+
+  expect(uidStatusPids).toEqual([entry.pid]);
+  expect(facts.map(({ identityAfter }) => identityAfter)).toMatchObject([
+    { state: "readable", effectiveUid: 1001 },
+    { state: "readable" },
+  ]);
+  expect(facts[1]?.identityAfter).not.toHaveProperty("effectiveUid");
+  expect(statReads).toEqual(
+    new Map([
+      [entry.pid, 3],
+      [43, 2],
+    ]),
+  );
+});
+
 it("reports absence only when /proc lookup and signal-zero both report ESRCH", async () => {
   const host = createSystemProcessOwnershipHost("linux", {});
   const signalProbe = vi.spyOn(process, "kill").mockImplementation(() => {
diff --git a/src/process/ProcessOwnership.sweepExit.test.ts b/src/process/ProcessOwnership.sweepExit.test.ts
new file mode 100644
index 0000000000..fb0b9b2f84
--- /dev/null
+++ b/src/process/ProcessOwnership.sweepExit.test.ts
@@ -0,0 +1,74 @@
+import { expect, it, vi } from "vitest";
+import {
+  verifyNoTokenOwnedProcesses,
+  type ProcessIdentityObservation,
+  type ProcessOwnershipHost,
+  type ProcessTableEntry,
+} from "./ProcessOwnership.js";
+import { ProcessOwnershipEvidenceOwner } from "./ProcessOwnershipEvidence.js";
+
+it.each(["absent", "zombie", "live", "unavailable"] as const)(
+  "settles a baseline candidate against its final native lifetime: %s",
+  async (lifetime) => {
+    const row: ProcessTableEntry = {
+      pid: 910,
+      parentPid: 1,
+      processGroupId: 910,
+      state: "S",
+      command: "baseline-neighbor",
+    };
+    let tokenRead = false;
+    const identity = (): ProcessIdentityObservation => {
+      if (lifetime === "absent")
+        return { state: "absent", reason: "not-in-snapshot" };
+      if (lifetime === "unavailable")
+        return { state: "unavailable", reason: "native identity denied" };
+      return {
+        state: "readable",
+        identity: "new-generation",
+        lifecycle: {
+          state: "observed",
+          lifecycle:
+            tokenRead && lifetime === "zombie" ? "zombie" : "non-zombie",
+        },
+        relation: { state: "observed", parentPid: 1, processGroupId: 910 },
+      };
+    };
+    const signalGroup = vi.fn();
+    const host: ProcessOwnershipHost = {
+      platform: "darwin",
+      listProcesses: async () => [row],
+      processIdentities: async (members) =>
+        new Map(members.map(({ pid }) => [pid, identity()])),
+      runTokens: async (members) => {
+        tokenRead = true;
+        return new Map(
+          members.map(({ pid }) => [
+            pid,
+            { state: "unavailable" as const, reason: "EACCES" },
+          ]),
+        );
+      },
+      environment: async () => ({}),
+      signalGroup,
+    };
+    const result = await verifyNoTokenOwnedProcesses(
+      "run",
+      host,
+      [{ pid: row.pid, identity: "baseline-generation" }],
+      {
+        leaderPid: 100,
+        processGroupId: 100,
+        evidenceOwner: new ProcessOwnershipEvidenceOwner(),
+      },
+    );
+    if (lifetime === "absent" || lifetime === "zombie")
+      expect(result).toEqual({ cleaned: true, signaled: false });
+    else
+      expect(result).toMatchObject({
+        cleaned: false,
+        failures: [{ pid: row.pid }],
+      });
+    expect(signalGroup).not.toHaveBeenCalled();
+  },
+);
diff --git a/src/process/ProcessOwnership.ts b/src/process/ProcessOwnership.ts
index 3cc3d6ee22..307b20220c 100644
--- a/src/process/ProcessOwnership.ts
+++ b/src/process/ProcessOwnership.ts
@@ -179,6 +179,8 @@ export interface ProcessOwnershipHost {
   processIdentities?(
     processes: readonly ProcessTableEntry[],
     signal?: AbortSignal,
+    /** Linux UID enrichment is selective; omitted means UID remains unknown. */
+    effectiveUidPids?: ReadonlySet<number>,
   ): Promise<ReadonlyMap<number, ProcessIdentityObservation>>;
   /** Snapshot identities before launch, honoring startup cancellation. */
   captureBaseline?(signal?: AbortSignal): Promise<ProcessOwnershipBaseline>;
@@ -965,6 +967,14 @@ const sanitizedTokenReadFailure = (diagnostic: string | undefined): string => {
   return "other_unavailable";
 };
 
+const processIdentityHasExited = (
+  identity: ProcessIdentityObservation,
+): boolean =>
+  identity.state === "absent" ||
+  (identity.state === "readable" &&
+    identity.lifecycle?.state === "observed" &&
+    identity.lifecycle.lifecycle === "zombie");
+
 const processOwnershipFailures = async (
   members: readonly ProcessTableEntry[],
   runId: string,
@@ -975,13 +985,7 @@ const processOwnershipFailures = async (
     const facts = await readProcessOwnershipFacts(members, host);
     const failures: ProcessOwnershipValidationFailure[] = [];
     for (const fact of facts) {
-      if (fact.identityAfter.state === "absent") continue;
-      if (
-        fact.identityAfter.state === "readable" &&
-        fact.identityAfter.lifecycle?.state === "observed" &&
-        fact.identityAfter.lifecycle.lifecycle === "zombie"
-      )
-        continue;
+      if (processIdentityHasExited(fact.identityAfter)) continue;
       const relation =
         fact.identityAfter.state === "readable" &&
         fact.identityAfter.relation?.state === "observed"
@@ -1289,14 +1293,17 @@ const scanWithOwnershipEvidence = async (
     observationRows,
     host,
   );
-  const baselineIdentityFailures: ProcessOwnershipValidationFailure[] = [];
+  const baselineIdentityFailures = new Map<
+    number,
+    ProcessOwnershipValidationFailure
+  >();
   const candidates = observationRows.filter((process) => {
     if (retainedPids.has(process.pid)) return true;
     if (!baseline.has(process.pid)) return true;
     const before = baseline.get(process.pid);
     const now = firstIdentities.get(process.pid);
     if (before === null || now?.state !== "readable") {
-      baselineIdentityFailures.push({
+      baselineIdentityFailures.set(process.pid, {
         pid: process.pid,
         reason: "process-identity-unavailable",
         diagnostic: "process identity was unavailable during token validation",
@@ -1320,21 +1327,18 @@ const scanWithOwnershipEvidence = async (
     },
   );
   let facts = initialFacts;
-  for (
-    let attempt = 0;
-    attempt < TOKEN_READ_RETRY_ATTEMPTS &&
-    facts.some(({ token }) => token.state === "unavailable");
-    attempt += 1
-  ) {
+  for (let attempt = 0; attempt < TOKEN_READ_RETRY_ATTEMPTS; attempt += 1) {
+    const retryRows = facts
+      .filter(
+        ({ token, identityAfter }) =>
+          token.state === "unavailable" &&
+          !processIdentityHasExited(identityAfter),
+      )
+      .map(({ process }) => process);
+    if (retryRows.length === 0) break;
     await new Promise<void>((resolve) =>
       setTimeout(resolve, TOKEN_READ_RETRY_DELAY_MS),
     );
-    const pendingPids = new Set(
-      facts
-        .filter(({ token }) => token.state === "unavailable")
-        .map(({ process }) => process.pid),
-    );
-    const retryRows = candidates.filter(({ pid }) => pendingPids.has(pid));
     const retries = await readProcessOwnershipFacts(retryRows, host);
     const retryByPid = new Map(retries.map((fact) => [fact.process.pid, fact]));
     facts = facts.map((fact) => retryByPid.get(fact.process.pid) ?? fact);
@@ -1356,24 +1360,26 @@ const scanWithOwnershipEvidence = async (
   const retainedByPid = new Map(
     retained.map((candidate) => [candidate.pid, candidate]),
   );
-  const failures: ProcessOwnershipValidationFailure[] = [
-    ...baselineIdentityFailures,
-  ];
+  const failures: ProcessOwnershipValidationFailure[] = [];
   const unverified: OwnershipSweepUnverifiedProcess[] = [];
   const owned: ProcessTableEntry[] = [];
   const identities = new Map<number, string | null>();
 
   for (const fact of facts) {
+    // The table row and baseline predate the final native observation. An
+    // exited candidate needs no ownership proof or signal, even when its
+    // token became unreadable while exiting. Unknown native state stays a
+    // cleanup failure; table omission alone is never proof of exit.
+    if (processIdentityHasExited(fact.identityAfter)) continue;
+    const baselineFailure = baselineIdentityFailures.get(fact.process.pid);
+    if (baselineFailure !== undefined) failures.push(baselineFailure);
     if (fact.state === "replaced")
       failures.push({
         pid: fact.process.pid,
         reason: "process-identity-unavailable",
         diagnostic: "process identity changed during token validation",
       });
-    else if (
-      fact.state === "unavailable" &&
-      fact.identityAfter.state !== "absent"
-    )
+    else if (fact.state === "unavailable")
       failures.push({
         pid: fact.process.pid,
         reason: "process-identity-unavailable",
@@ -1392,7 +1398,6 @@ const scanWithOwnershipEvidence = async (
         reason: "run-token-mismatch",
       });
     if (fact.token.state !== "unavailable") continue;
-    if (fact.identityAfter.state === "absent") continue;
     const relationBefore =
       fact.identityBefore.state === "readable"
         ? fact.identityBefore.relation
diff --git a/src/process/ProcessOwnershipObservation.ts b/src/process/ProcessOwnershipObservation.ts
index 592833855d..01439da94f 100644
--- a/src/process/ProcessOwnershipObservation.ts
+++ b/src/process/ProcessOwnershipObservation.ts
@@ -1,5 +1,6 @@
 import { readFile } from "node:fs/promises";
 import { parseLinuxProcessStat } from "./LinuxProcessStat.js";
+import { parseLinuxProcessEffectiveUid } from "./LinuxProcessStatus.js";
 import { AnalysisCapabilityUnavailableError } from "../domain/analysisErrorCore.js";
 
 import { launcherIdentityFailure } from "./ProcessOwnershipIdentity.js";
@@ -498,6 +499,7 @@ const readIdentityFacts = async (
   host: ProcessOwnershipHost,
   phase: "before" | "after",
   signal?: AbortSignal,
+  effectiveUidPids?: ReadonlySet<number>,
 ): Promise<ReadonlyMap<number, ProcessIdentityObservation>> => {
   signal?.throwIfAborted();
   if (host.processIdentities === undefined)
@@ -511,10 +513,11 @@ const readIdentityFacts = async (
       ]),
     );
   try {
-    const observations =
-      signal === undefined
-        ? await host.processIdentities(processes)
-        : await host.processIdentities(processes, signal);
+    const observations = await host.processIdentities(
+      processes,
+      signal,
+      effectiveUidPids,
+    );
     signal?.throwIfAborted();
     return new Map<number, ProcessIdentityObservation>(
       processes.map(({ pid }) => [pid, identityFact(observations, pid, phase)]),
@@ -583,11 +586,17 @@ export const readProcessOwnershipFacts = async (
   }
   signal?.throwIfAborted();
 
+  const effectiveUidPids = new Set(
+    processes
+      .filter(({ pid }) => tokens.get(pid)?.state !== "readable")
+      .map(({ pid }) => pid),
+  );
   const identityAfter = await readIdentityFacts(
     processes,
     host,
     "after",
     signal,
+    effectiveUidPids,
   );
   signal?.throwIfAborted();
   const facts = processes.map((process): ProcessOwnershipFact => {
@@ -699,7 +708,7 @@ export const createSystemProcessOwnershipHost = (
   };
   const processIdentities: NonNullable<
     ProcessOwnershipHost["processIdentities"]
-  > = async (processes, signal) => {
+  > = async (processes, signal, effectiveUidPids) => {
     if (processes.length === 0) return new Map();
     if (platform === "linux")
       return new Map<number, ProcessIdentityObservation>(
@@ -716,27 +725,78 @@ export const createSystemProcessOwnershipHost = (
                 ...(signal === undefined ? {} : { signal }),
               });
               const parsed = parseLinuxProcessStat(stat);
-              return [
-                pid,
-                parsed === undefined || parsed.pid !== pid
-                  ? ({
-                      state: "unavailable",
-                      reason: "malformed_proc_stat",
-                    } as const)
-                  : ({
-                      state: "readable",
-                      identity: `linux-starttime:${parsed.startTime}`,
-                      lifecycle: {
-                        state: "observed",
-                        lifecycle: parsed.lifecycle,
-                      },
-                      relation: {
-                        state: "observed",
-                        parentPid: parsed.parentPid,
-                        processGroupId: parsed.processGroupId,
-                      },
-                    } as const),
-              ] as const;
+              if (parsed === undefined || parsed.pid !== pid)
+                return [
+                  pid,
+                  {
+                    state: "unavailable",
+                    reason: "malformed_proc_stat",
+                  } as const,
+                ] as const;
+
+              const readableIdentity = (
+                facts: typeof parsed,
+                effectiveUid?: number,
+              ) => ({
+                state: "readable" as const,
+                identity: `linux-starttime:${facts.startTime}`,
+                ...(effectiveUid === undefined ? {} : { effectiveUid }),
+                lifecycle: {
+                  state: "observed" as const,
+                  lifecycle: facts.lifecycle,
+                },
+                relation: {
+                  state: "observed" as const,
+                  parentPid: facts.parentPid,
+                  processGroupId: facts.processGroupId,
+                },
+              });
+
+              if (!effectiveUidPids?.has(pid))
+                return [pid, readableIdentity(parsed)] as const;
+
+              let status: string;
+              try {
+                status = await readFile(`/proc/${String(pid)}/status`, {
+                  encoding: "utf8",
+                  ...(signal === undefined ? {} : { signal }),
+                });
+              } catch (cause: unknown) {
+                if (isExpectedAbort(cause, signal)) throw cause;
+                return [pid, readableIdentity(parsed)] as const;
+              }
+              signal?.throwIfAborted();
+              const effectiveUid = parseLinuxProcessEffectiveUid(status);
+              if (effectiveUid === undefined)
+                return [pid, readableIdentity(parsed)] as const;
+
+              let afterStatus: string;
+              try {
+                afterStatus = await readFile(`/proc/${String(pid)}/stat`, {
+                  encoding: "utf8",
+                  ...(signal === undefined ? {} : { signal }),
+                });
+              } catch (cause: unknown) {
+                if (isExpectedAbort(cause, signal)) throw cause;
+                return [pid, readableIdentity(parsed)] as const;
+              }
+              signal?.throwIfAborted();
+              const verified = parseLinuxProcessStat(afterStatus);
+              if (
+                verified !== undefined &&
+                verified.pid === pid &&
+                verified.startTime !== parsed.startTime
+              )
+                return [
+                  pid,
+                  {
+                    state: "unavailable",
+                    reason: "process_identity_changed_during_uid_observation",
+                  } as const,
+                ] as const;
+              if (verified === undefined || verified.pid !== pid)
+                return [pid, readableIdentity(parsed)] as const;
+              return [pid, readableIdentity(verified, effectiveUid)] as const;
             } catch (cause: unknown) {
               if (isExpectedAbort(cause, signal)) throw cause;
               if (
diff --git a/tests/boundary/filesystem/packageSetupPlanDiagnostics.test.ts b/tests/boundary/filesystem/packageSetupPlanDiagnostics.test.ts
new file mode 100644
index 0000000000..7de7c1d420
--- /dev/null
+++ b/tests/boundary/filesystem/packageSetupPlanDiagnostics.test.ts
@@ -0,0 +1,39 @@
+import { expect, it } from "vitest";
+
+import { setupPlanFailureMessage } from "../../../scripts/verify-package-setup-plan.mjs";
+
+it("preserves setup failure details when an error result has no action arrays", () => {
+  const result = {
+    status: "needs_human",
+    remediation: "Review the host setup requirements.",
+  };
+  const message = setupPlanFailureMessage({
+    planned: result,
+    plannedExecution: { status: 1 },
+    plannedClaudeConfig: "unchanged",
+    plannedCodexConfig: "unchanged",
+    plannedCursorConfig: "unchanged",
+  });
+
+  expect(message).toContain("packaged setup plan was not read-only");
+  expect(message).toContain('"status":"needs_human"');
+  expect(message).toContain("Review the host setup requirements.");
+  expect(message).not.toContain("TypeError");
+});
+
+it("still formats action kinds for a structured setup result", () => {
+  const message = setupPlanFailureMessage({
+    planned: {
+      status: "planned",
+      plannedActions: [{ kind: "configure_client" }],
+      appliedActions: [],
+    },
+    plannedExecution: { status: 0 },
+    plannedClaudeConfig: "unchanged",
+    plannedCodexConfig: "unchanged",
+    plannedCursorConfig: "unchanged",
+  });
+
+  expect(message).toContain('"plannedKinds":["configure_client"]');
+  expect(message).toContain('"appliedKinds":[]');
+});
diff --git a/tests/boundary/filesystem/recordedCrashTraceClassifier.test.ts b/tests/boundary/filesystem/recordedCrashTraceClassifier.test.ts
new file mode 100644
index 0000000000..f03fbd5ba1
--- /dev/null
+++ b/tests/boundary/filesystem/recordedCrashTraceClassifier.test.ts
@@ -0,0 +1,144 @@
+import { expect, it } from "vitest";
+
+import { assertHistoricalPidReadsAreOwnershipOnly } from "../../../scripts/verify/recorded-crash/trace-ownership.mjs";
+
+const psExec =
+  'execve("/usr/bin/ps", ["ps", "-axo", "pid=,ppid=,pgid=,uid=,stat=,command="], 0x7fff) = 0';
+
+it("correlates the ps child trace with its parent identity read", () => {
+  const ownershipReads = assertHistoricalPidReadsAreOwnershipOnly({
+    sentinelPid: 4008,
+    psExecutables: new Set(["/usr/bin/ps"]),
+    traces: [
+      {
+        pid: 1200,
+        text: [
+          "vfork() = 1201",
+          "clone3({flags=CLONE_VM|CLONE_SIGHAND|CLONE_THREAD}, 88) = 1202",
+          'openat(AT_FDCWD, "/proc/4008/stat", O_RDONLY|O_CLOEXEC) = 21',
+        ].join("\n"),
+      },
+      {
+        pid: 1202,
+        text: [
+          'openat(AT_FDCWD, "/proc/4008/stat", O_RDONLY|O_CLOEXEC) = 21',
+          'openat(AT_FDCWD, "/proc/4008/status", O_RDONLY|O_CLOEXEC) = 22',
+        ].join("\n"),
+      },
+      {
+        pid: 1201,
+        text: [
+          psExec,
+          'openat(AT_FDCWD, "/proc/4008/status", O_RDONLY) = 3',
+          'openat(AT_FDCWD, "/proc/4008/cmdline", O_RDONLY) = 4',
+        ].join("\n"),
+      },
+    ],
+  });
+
+  expect(ownershipReads).toHaveLength(5);
+});
+
+it("joins unfinished and resumed CLONE_THREAD records", () => {
+  const ownershipReads = assertHistoricalPidReadsAreOwnershipOnly({
+    sentinelPid: 4008,
+    psExecutables: new Set(["/usr/bin/ps"]),
+    traces: [
+      {
+        pid: 1200,
+        text: [
+          "vfork() = 1201",
+          "clone3({flags=CLONE_VM|CLONE_SIGHAND|CLONE_THREAD, child_tid=0x3 <unfinished ...>",
+          "<... clone3 resumed>) = 1202",
+        ].join("\n"),
+      },
+      {
+        pid: 1202,
+        text: 'openat(AT_FDCWD, "/proc/4008/stat", O_RDONLY) = 3',
+      },
+      { pid: 1201, text: psExec },
+    ],
+  });
+
+  expect(ownershipReads).toHaveLength(1);
+});
+
+it("rejects provider-style reads outside the ps child and stat-only caller", () => {
+  const traces = [
+    {
+      pid: 1200,
+      text: [
+        "vfork() = 1201",
+        'openat(AT_FDCWD, "/proc/4008/cmdline", O_RDONLY) = 21',
+      ].join("\n"),
+    },
+    { pid: 1201, text: psExec },
+  ];
+
+  expect(() =>
+    assertHistoricalPidReadsAreOwnershipOnly({
+      traces,
+      sentinelPid: 4008,
+      psExecutables: new Set(["/usr/bin/ps"]),
+    }),
+  ).toThrow("Historical PID caused a provider lookup");
+});
+
+it("does not trust a ps command with different arguments or failed exec", () => {
+  for (const text of [
+    'execve("/usr/bin/ps", ["ps", "-ef"], 0x7fff) = 0',
+    psExec.replace(" = 0", " = -1 EACCES"),
+  ])
+    expect(() =>
+      assertHistoricalPidReadsAreOwnershipOnly({
+        sentinelPid: 4008,
+        psExecutables: new Set(["/usr/bin/ps"]),
+        traces: [
+          {
+            pid: 1200,
+            text: `vfork() = 1201\nopenat(AT_FDCWD, "/proc/4008/stat", O_RDONLY) = 3`,
+          },
+          { pid: 1201, text },
+        ],
+      }),
+    ).toThrow("Historical PID caused a provider lookup");
+});
+
+it("allows only known procfs fields inside the exact ps child", () => {
+  expect(() =>
+    assertHistoricalPidReadsAreOwnershipOnly({
+      sentinelPid: 4008,
+      psExecutables: new Set(["/usr/bin/ps"]),
+      traces: [
+        { pid: 1200, text: "vfork() = 1201" },
+        {
+          pid: 1201,
+          text: `${psExec}\nopenat(AT_FDCWD, "/proc/4008/exe", O_RDONLY) = 3`,
+        },
+      ],
+    }),
+  ).toThrow("Historical PID caused a provider lookup");
+});
+
+it("does not grant the ownership process thread permit to a forked child", () => {
+  for (const field of ["stat", "status"])
+    expect(() =>
+      assertHistoricalPidReadsAreOwnershipOnly({
+        sentinelPid: 4008,
+        psExecutables: new Set(["/usr/bin/ps"]),
+        traces: [
+          {
+            pid: 1200,
+            text: ["vfork() = 1201", "clone3({flags=SIGCHLD}, 88) = 1203"].join(
+              "\n",
+            ),
+          },
+          { pid: 1201, text: psExec },
+          {
+            pid: 1203,
+            text: `openat(AT_FDCWD, "/proc/4008/${field}", O_RDONLY) = 3`,
+          },
+        ],
+      }),
+    ).toThrow("Historical PID caused a provider lookup");
+});
diff --git a/tests/boundary/mcp/advertisedPatternsVMode.test.ts b/tests/boundary/mcp/advertisedPatternsVMode.test.ts
index b48fe27aa0..1291d79d9a 100644
--- a/tests/boundary/mcp/advertisedPatternsVMode.test.ts
+++ b/tests/boundary/mcp/advertisedPatternsVMode.test.ts
@@ -1,7 +1,14 @@
 import { Client, InMemoryTransport } from "@modelcontextprotocol/client";
+import { AjvJsonSchemaValidator } from "@modelcontextprotocol/client/validators/ajv";
 import { expect, it, onTestFinished } from "vitest";
 
 import { createServer } from "../../../src/server/createServer.js";
+import {
+  BASE64_QUARTET_LENGTH_PATTERN,
+  INVALID_BASE64_CHARACTER_PATTERN,
+  INVALID_BASE64_PADDING_PATTERN,
+  INVALID_CANONICAL_BASE64_PAD_BITS_PATTERN,
+} from "../../../src/domain/stringPatterns.js";
 import { createTestBinarySession } from "../../fixtures/binarySession.js";
 
 interface AdvertisedPattern {
@@ -10,6 +17,33 @@ interface AdvertisedPattern {
   readonly pattern: string;
 }
 
+const collectCanonicalBase64Leaves = (
+  value: unknown,
+  leaves: Record<string, unknown>[],
+): void => {
+  if (value === null || typeof value !== "object") return;
+  if (Array.isArray(value)) {
+    value.forEach((entry) => collectCanonicalBase64Leaves(entry, leaves));
+    return;
+  }
+  const record = value as Record<string, unknown>;
+  const allOf = record.allOf;
+  if (
+    Array.isArray(allOf) &&
+    allOf.some(
+      (entry) =>
+        entry !== null &&
+        typeof entry === "object" &&
+        "pattern" in entry &&
+        entry.pattern === BASE64_QUARTET_LENGTH_PATTERN.source,
+    )
+  )
+    leaves.push(record);
+  Object.values(record).forEach((entry) =>
+    collectCanonicalBase64Leaves(entry, leaves),
+  );
+};
+
 const collectPatterns = (
   value: unknown,
   where: string,
@@ -48,12 +82,29 @@ it("advertises portable NUL escapes and patterns that compile in all JS modes",
 
   const advertised = (await client.listTools()).tools;
   const patterns: AdvertisedPattern[] = [];
+  const canonicalBase64Leaves: Record<string, unknown>[] = [];
   for (const tool of advertised) {
     collectPatterns(tool.inputSchema, "inputSchema", tool.name, patterns);
+    collectCanonicalBase64Leaves(tool.inputSchema, canonicalBase64Leaves);
     if (tool.outputSchema !== undefined)
       collectPatterns(tool.outputSchema, "outputSchema", tool.name, patterns);
+    if (tool.outputSchema !== undefined)
+      collectCanonicalBase64Leaves(tool.outputSchema, canonicalBase64Leaves);
   }
 
+  for (const pattern of [
+    BASE64_QUARTET_LENGTH_PATTERN,
+    INVALID_BASE64_CHARACTER_PATTERN,
+    INVALID_BASE64_PADDING_PATTERN,
+    INVALID_CANONICAL_BASE64_PAD_BITS_PATTERN,
+  ])
+    expect(
+      patterns.some(({ pattern: advertisedPattern }) =>
+        advertisedPattern.includes(pattern.source),
+      ),
+      pattern.source,
+    ).toBe(true);
+
   // Annex B and `u` mode accept an unescaped `-`, `/` or `[` inside a character
   // class, so REA's own schema validation cannot observe the defect. `v` mode
   // rejects them, and a client that compiles advertised patterns rejects the
@@ -87,4 +138,19 @@ it("advertises portable NUL escapes and patterns that compile in all JS modes",
     ),
   ).toEqual([]);
   expect(patterns.some(({ pattern }) => pattern.includes("\\x00"))).toBe(true);
+
+  expect(canonicalBase64Leaves.length).toBeGreaterThan(0);
+  const sdkValidator = new AjvJsonSchemaValidator();
+  const validators = canonicalBase64Leaves.map((schema) =>
+    sdkValidator.getValidator(schema),
+  );
+  for (const value of ["", "AA==", "AQID", "AB==", "AAA", "AA$=", "AA\n=="])
+    expect(
+      validators.map((validate) => validate(value).valid),
+      JSON.stringify(value),
+    ).toEqual(
+      canonicalBase64Leaves.map(
+        () => value === "" || value === "AA==" || value === "AQID",
+      ),
+    );
 });