diff --git a/CHANGELOG.md b/CHANGELOG.md
index bcd8827..7b3f591 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,18 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Added
+
+- **Safe Prune Inspection**: Added `inspectPrunableObjects()` for streaming the
+  loose unreachable objects Git would prune before a canonical UTC cutoff.
+
+### Fixed
+
+- **Sanitizer Memoization**: Replaced the lossy command-cache key so commands
+  with different safety properties cannot collide.
+
 ## [3.0.3] - 2026-05-06
 
 ### Fixed
diff --git a/README.md b/README.md
index 13fda32..4978fa2 100644
--- a/README.md
+++ b/README.md
@@ -74,6 +74,24 @@ const commitSha = await git.createCommitFromFiles({
 });
 ```
 
+### Non-Mutating Prune Inspection
+
+Stream loose unreachable objects that Git considers older than a canonical UTC
+cutoff. This API always invokes Git with `--dry-run --no-progress`;
+unrestricted `git prune` remains prohibited by the command sanitizer.
+
+```javascript
+const plumbing = await GitPlumbing.createDefault({ cwd: './my-repo' });
+const stream = await plumbing.inspectPrunableObjects({
+  expiresBefore: '2026-07-01T00:00:00.000Z'
+});
+
+for await (const chunk of stream) {
+  // Parse Git's `<object-id> <type>` records incrementally.
+}
+await stream.finished;
+```
+
 ## 📖 Deep Dives
 
 - [**Standard Guide**](./GUIDE.md) - From zero to atomic commits.
diff --git a/index.js b/index.js
index 9ffe32b..2b36d15 100644
--- a/index.js
+++ b/index.js
@@ -28,6 +28,27 @@ import GitPersistenceService from './src/domain/services/GitPersistenceService.j
 // Infrastructure
 import GitStream from './src/infrastructure/GitStream.js';
 
+const CANONICAL_UTC_TIMESTAMP = /^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}Z$/;
+
+function normalizePruneExpiry(expiresBefore) {
+  if (typeof expiresBefore !== 'string' || !CANONICAL_UTC_TIMESTAMP.test(expiresBefore)) {
+    throw new InvalidArgumentError(
+      'expiresBefore must be a canonical UTC timestamp',
+      'GitPlumbing.inspectPrunableObjects',
+      { expiresBefore }
+    );
+  }
+  const parsed = Date.parse(expiresBefore);
+  if (!Number.isFinite(parsed) || new Date(parsed).toISOString() !== expiresBefore) {
+    throw new InvalidArgumentError(
+      'expiresBefore must be a valid canonical UTC timestamp',
+      'GitPlumbing.inspectPrunableObjects',
+      { expiresBefore }
+    );
+  }
+  return expiresBefore;
+}
+
 /**
  * Named exports for public API
  */
@@ -199,6 +220,21 @@ export default class GitPlumbing {
     }
   }
 
+  /**
+   * Streams the loose unreachable objects Git would prune before a cutoff.
+   * The command is unconditionally dry-run and never mutates repository state.
+   *
+   * @param {Object} options
+   * @param {string} options.expiresBefore - Canonical UTC timestamp.
+   * @returns {Promise<GitStream>}
+   */
+  async inspectPrunableObjects({ expiresBefore } = {}) {
+    const expiry = normalizePruneExpiry(expiresBefore);
+    return await this.executeStream({
+      args: ['prune', '--dry-run', '--verbose', '--no-progress', `--expire=${expiry}`]
+    });
+  }
+
   /**
    * Executes a git command and returns both stdout and exit status without throwing on non-zero exit.
    * @param {Object} options
diff --git a/src/domain/services/CommandSanitizer.js b/src/domain/services/CommandSanitizer.js
index e2facfa..ff8903d 100644
--- a/src/domain/services/CommandSanitizer.js
+++ b/src/domain/services/CommandSanitizer.js
@@ -44,7 +44,8 @@ export default class CommandSanitizer {
     'init',
     'config',
     'log',
-    'show'
+    'show',
+    'prune'
   ]);
 
   /**
@@ -98,9 +99,35 @@ export default class CommandSanitizer {
       '--graph', '--decorate', '--no-decorate', '--source',
       '--no-walk', '--stdin', '--cherry', '--cherry-pick', '--cherry-mark',
       '--boundary', '--simplify-by-decoration'
+    ]),
+    'prune': new Set([
+      '--dry-run', '-n', '--verbose', '-v', '--no-progress', '--expire'
     ])
   };
 
+  /**
+   * Enforces command-level safety requirements that a flag allowlist cannot
+   * express by itself.
+   * @param {string} command
+   * @param {string[]} args
+   * @param {number} commandIndex
+   * @throws {ProhibitedFlagError} If a command omits a required safety flag
+   * @private
+   */
+  static _validateCommandSafety(command, args, commandIndex) {
+    if (command !== 'prune') {
+      return;
+    }
+    const commandArgs = args.slice(commandIndex + 1);
+    const endOfOptions = commandArgs.indexOf('--');
+    const flags = endOfOptions === -1 ? commandArgs : commandArgs.slice(0, endOfOptions);
+    if (!flags.includes('--dry-run') && !flags.includes('-n')) {
+      throw new ProhibitedFlagError('prune', 'CommandSanitizer.sanitize', {
+        message: "The 'prune' command is allowed only with --dry-run or -n"
+      });
+    }
+  }
+
   /**
    * Validates command-specific flags against the allowlist.
    * @param {string} command - The git subcommand (e.g., 'show', 'log')
@@ -183,16 +210,31 @@ export default class CommandSanitizer {
       throw new ValidationError('Arguments array cannot be empty', 'CommandSanitizer.sanitize');
     }
 
-    // Memory-efficient cache key using a short structural signature
-    const cacheKey = `${args[0]}:${args.length}:${args[args.length-1]?.length || 0}:${args.join('').length}`;
-    if (this._cache.has(cacheKey)) {
-      return args;
-    }
-
     if (args.length > CommandSanitizer.MAX_ARGS) {
       throw new ValidationError(`Too many arguments: ${args.length}`, 'CommandSanitizer.sanitize');
     }
 
+    let totalLength = 0;
+    for (const arg of args) {
+      if (typeof arg !== 'string') {
+        throw new ValidationError('Each argument must be a string', 'CommandSanitizer.sanitize', { arg });
+      }
+      totalLength += arg.length;
+      if (arg.length > CommandSanitizer.MAX_ARG_LENGTH) {
+        throw new ValidationError(`Argument too long: ${arg.length}`, 'CommandSanitizer.sanitize');
+      }
+    }
+    if (totalLength > CommandSanitizer.MAX_TOTAL_LENGTH) {
+      throw new ValidationError(`Total arguments length too long: ${totalLength}`, 'CommandSanitizer.sanitize');
+    }
+
+    // The cache key must preserve every argument. A lossy structural key can
+    // collide across commands with different safety properties.
+    const cacheKey = JSON.stringify(args);
+    if (this._cache.has(cacheKey)) {
+      return args;
+    }
+
     // Special case: allow exactly ['--version'] as a global flag check
     if (args.length === 1 && args[0] === '--version') {
       return args;
@@ -202,9 +244,6 @@ export default class CommandSanitizer {
     let subcommandIndex = -1;
     for (let i = 0; i < args.length; i++) {
       const arg = args[i];
-      if (typeof arg !== 'string') {
-        throw new ValidationError('Each argument must be a string', 'CommandSanitizer.sanitize', { arg });
-      }
       if (!arg.startsWith('-')) {
         subcommandIndex = i;
         break;
@@ -236,19 +275,8 @@ export default class CommandSanitizer {
 
     // Validate per-command flag allowlists
     CommandSanitizer._validateCommandFlags(command, args, subcommandIndex !== -1 ? subcommandIndex : 0);
+    CommandSanitizer._validateCommandSafety(command, args, subcommandIndex !== -1 ? subcommandIndex : 0);
 
-    let totalLength = 0;
-    for (const arg of args) {
-      totalLength += arg.length;
-      if (arg.length > CommandSanitizer.MAX_ARG_LENGTH) {
-        throw new ValidationError(`Argument too long: ${arg.length}`, 'CommandSanitizer.sanitize');
-      }
-    }
-
-    if (totalLength > CommandSanitizer.MAX_TOTAL_LENGTH) {
-      throw new ValidationError(`Total arguments length too long: ${totalLength}`, 'CommandSanitizer.sanitize');
-    }
-    
     // Manage cache size
     if (this._cache.size >= this._maxCacheSize) {
       const firstKey = this._cache.keys().next().value;
@@ -258,4 +286,4 @@ export default class CommandSanitizer {
 
     return args;
   }
-}
\ No newline at end of file
+}
diff --git a/test/PruneInspection.test.js b/test/PruneInspection.test.js
new file mode 100644
index 0000000..ee511b3
--- /dev/null
+++ b/test/PruneInspection.test.js
@@ -0,0 +1,82 @@
+import fs from 'node:fs';
+import os from 'node:os';
+import path from 'node:path';
+import GitPlumbing from '../index.js';
+import InvalidArgumentError from '../src/domain/errors/InvalidArgumentError.js';
+
+describe('prunable-object inspection', () => {
+  let git;
+  let repoPath;
+
+  beforeEach(async () => {
+    repoPath = fs.mkdtempSync(path.join(os.tmpdir(), 'git-plumbing-prune-'));
+    git = await GitPlumbing.createDefault({ cwd: repoPath });
+    await git.execute({ args: ['init'] });
+  });
+
+  afterEach(() => {
+    fs.rmSync(repoPath, { recursive: true, force: true });
+  });
+
+  it('streams dry-run candidates without deleting them', async () => {
+    const oid = await git.execute({
+      args: ['hash-object', '-w', '--stdin'],
+      input: 'unreachable test object'
+    });
+    const expiresBefore = new Date(Date.now() + 60_000).toISOString();
+    const stream = await git.inspectPrunableObjects({ expiresBefore });
+    const output = await stream.collect({ asString: true });
+    const result = await stream.finished;
+
+    expect(result.code).toBe(0);
+    expect(output).toContain(`${oid} blob`);
+    await expect(git.execute({ args: ['cat-file', '-t', oid] })).resolves.toBe('blob');
+  });
+
+  it('constructs the complete non-mutating inspection command', async () => {
+    let invocation;
+    const plumbing = new GitPlumbing({
+      cwd: repoPath,
+      runner: async (options) => {
+        invocation = options;
+        return {
+          stdoutStream: new ReadableStream({
+            start(controller) {
+              controller.close();
+            }
+          }),
+          exitPromise: Promise.resolve({ code: 0, stderr: '' })
+        };
+      }
+    });
+    const expiresBefore = '2026-07-01T00:00:00.000Z';
+
+    const stream = await plumbing.inspectPrunableObjects({ expiresBefore });
+    await stream.collect();
+
+    expect(invocation.args).toEqual([
+      'prune',
+      '--dry-run',
+      '--verbose',
+      '--no-progress',
+      `--expire=${expiresBefore}`
+    ]);
+  });
+
+  for (const expiresBefore of [
+    undefined,
+    'now',
+    '2026-07-01',
+    '2026-13-01T00:00:00.000Z',
+    '2026-07-01T00:00:00Z'
+  ]) {
+    it(`rejects a non-canonical cutoff before execution: ${String(expiresBefore)}`, async () => {
+      await expect(git.inspectPrunableObjects({ expiresBefore }))
+        .rejects.toBeInstanceOf(InvalidArgumentError);
+    });
+  }
+
+  it('rejects omitted options with the public validation error', async () => {
+    await expect(git.inspectPrunableObjects()).rejects.toBeInstanceOf(InvalidArgumentError);
+  });
+});
diff --git a/test/deno_entry.js b/test/deno_entry.js
index e48cf01..a5e3c6e 100644
--- a/test/deno_entry.js
+++ b/test/deno_entry.js
@@ -6,6 +6,7 @@ import "./GitBlob.test.js";
 import "./GitCommitFlow.test.js";
 import "./GitRef.test.js";
 import "./GitSha.test.js";
+import "./PruneInspection.test.js";
 import "./ShellRunner.test.js";
 import "./StreamCompletion.test.js";
 import "./Streaming.test.js";
diff --git a/test/domain/services/CommandSanitizer.test.js b/test/domain/services/CommandSanitizer.test.js
index 001cc2e..71d2bd6 100644
--- a/test/domain/services/CommandSanitizer.test.js
+++ b/test/domain/services/CommandSanitizer.test.js
@@ -21,6 +21,34 @@ describe('CommandSanitizer', () => {
     expect(() => sanitizer.sanitize(['show', '--format=%B', '-s', 'HEAD'])).not.toThrow();
   });
 
+  it('allows prune only as a dry-run inspection', () => {
+    expect(() => sanitizer.sanitize([
+      'prune',
+      '--dry-run',
+      '--verbose',
+      '--no-progress',
+      '--expire=2026-07-01T00:00:00.000Z'
+    ])).not.toThrow();
+    expect(() => sanitizer.sanitize(['prune', '-n', '-v', '--expire=now'])).not.toThrow();
+  });
+
+  it('rejects destructive or unrestricted prune forms', () => {
+    expect(() => sanitizer.sanitize(['prune', '--verbose'])).toThrow(ProhibitedFlagError);
+    expect(() => sanitizer.sanitize(['prune', '--dry-run', '--expire=now', '--progress']))
+      .toThrow(ProhibitedFlagError);
+    expect(() => sanitizer.sanitize(['prune', '--', '--dry-run']))
+      .toThrow(ProhibitedFlagError);
+  });
+
+  it('does not confuse safe and destructive commands in the memoization cache', () => {
+    sanitizer.sanitize(['prune', '--dry-run']);
+    expect(() => sanitizer.sanitize(['prune', '--verbose'])).toThrow(ProhibitedFlagError);
+  });
+
+  it('validates argument types before constructing a memoization key', () => {
+    expect(() => sanitizer.sanitize(['rev-parse', 1n])).toThrow(ValidationError);
+  });
+
   it('throws ValidationError for unlisted commands', () => {
     expect(() => sanitizer.sanitize(['push', 'origin', 'main'])).toThrow(ValidationError);
   });
@@ -211,4 +239,4 @@ describe('CommandSanitizer', () => {
       expect(() => sanitizer.sanitize(['show', '-p', '--', 'file.txt'])).toThrow(ProhibitedFlagError);
     });
   });
-});
\ No newline at end of file
+});