diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index ce3b3349..fa653501 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -76,3 +76,21 @@ jobs:
 
     - name: Integration Tests
       run: composer test:integration
+
+    # tests-tia records coverage inside its sandbox, which requires
+    # pcov (or xdebug) in the process PHP. The main setup-php step is
+    # `coverage: none` for speed — re-enable pcov here just for the
+    # TIA step. Cheap: pcov startup is near-zero.
+    - name: Enable pcov for TIA
+      uses: shivammathur/setup-php@v2
+      with:
+        php-version: ${{ matrix.php }}
+        tools: composer:v2
+        coverage: pcov
+        extensions: sockets
+
+    - name: TIA End-to-End Tests
+      # Black-box tests drive Pest `--tia` against a throw-away sandbox.
+      # First scenario takes ~60s (composer-installs the host Pest into a
+      # cached template); subsequent clones are cheap.
+      run: composer test:tia
diff --git a/bin/pest b/bin/pest
index 8cd27788..10a65dd0 100755
--- a/bin/pest
+++ b/bin/pest
@@ -142,6 +142,15 @@ use Symfony\Component\Console\Output\ConsoleOutput;
 
     // Get $rootPath based on $autoloadPath
     $rootPath = dirname($autoloadPath, 2);
+
+    // Re-execs PHP without Xdebug on TIA replay runs so repeat `--tia`
+    // invocations aren't slowed by a coverage driver they don't use. Plain
+    // `pest` runs are left alone — users may rely on Xdebug for IDE
+    // breakpoints, step-through debugging, or custom tooling. See
+    // XdebugGuard for the full decision (coverage / tia-rebuild / Xdebug
+    // mode gates).
+    \Pest\Support\XdebugGuard::maybeDrop($rootPath);
+
     $input = new ArgvInput;
 
     $testSuite = TestSuite::getInstance(
diff --git a/composer.json b/composer.json
index 1f3eadf2..c9dc5eb3 100644
--- a/composer.json
+++ b/composer.json
@@ -19,6 +19,7 @@
     "require": {
         "php": "^8.3.0",
         "brianium/paratest": "^7.20.0",
+        "composer/xdebug-handler": "^3.0.5",
         "nunomaduro/collision": "^8.9.4",
         "nunomaduro/termwind": "^2.4.0",
         "pestphp/pest-plugin": "^4.0.0",
@@ -92,6 +93,7 @@
         "test:inline": "php bin/pest --configuration=phpunit.inline.xml",
         "test:parallel": "php bin/pest --exclude-group=integration --parallel --processes=3",
         "test:integration": "php bin/pest --group=integration -v",
+        "test:tia": "php bin/pest --configuration=tests-tia/phpunit.xml",
         "update:snapshots": "REBUILD_SNAPSHOTS=true php bin/pest --update-snapshots",
         "test": [
             "@test:lint",
@@ -99,7 +101,8 @@
             "@test:type:coverage",
             "@test:unit",
             "@test:parallel",
-            "@test:integration"
+            "@test:integration",
+            "@test:tia"
         ]
     },
     "extra": {
diff --git a/src/Plugins/Tia.php b/src/Plugins/Tia.php
index e66ee239..9a57f5ab 100644
--- a/src/Plugins/Tia.php
+++ b/src/Plugins/Tia.php
@@ -74,6 +74,14 @@ final class Tia implements AddsOutput, HandlesArguments, Terminable
 
     private const string REBUILD_OPTION = '--tia-rebuild';
 
+    /**
+     * Bypasses `BaselineSync`'s post-failure cooldown. After a failed
+     * baseline fetch, subsequent `--tia` runs skip the fetch for 24h; this
+     * flag forces an immediate retry (e.g. right after publishing a
+     * baseline from CI for the first time).
+     */
+    private const string REFETCH_OPTION = '--tia-refetch';
+
     /**
      * State keys under which TIA persists its blobs. Kept here as constants
      * (rather than scattered strings) so the storage layout is visible in
@@ -103,6 +111,14 @@ final class Tia implements AddsOutput, HandlesArguments, Terminable
      */
     public const string KEY_COVERAGE_MARKER = 'coverage.marker';
 
+    /**
+     * Cooldown marker keyed by `BaselineSync` after a failed fetch. Holds
+     * `{"until": <unix>}` — subsequent runs within the window skip the
+     * fetch attempt (and its `gh run list` network hop) until the
+     * cooldown expires or the user passes `--tia-refetch`.
+     */
+    public const string KEY_FETCH_COOLDOWN = 'fetch-cooldown.json';
+
     /**
      * Global flag toggled by the parent process so workers know to record.
      */
@@ -199,6 +215,12 @@ final class Tia implements AddsOutput, HandlesArguments, Terminable
      */
     private bool $recordingActive = false;
 
+    /**
+     * True when `--tia-refetch` is in the current argv — `BaselineSync`
+     * uses it to bypass the post-failure fetch cooldown.
+     */
+    private bool $forceRefetch = false;
+
     public function __construct(
         private readonly OutputInterface $output,
         private readonly Recorder $recorder,
@@ -310,13 +332,15 @@ final class Tia implements AddsOutput, HandlesArguments, Terminable
 
         $enabled = $this->hasArgument(self::OPTION, $arguments);
         $forceRebuild = $this->hasArgument(self::REBUILD_OPTION, $arguments);
+        $this->forceRefetch = $this->hasArgument(self::REFETCH_OPTION, $arguments);
 
-        if (! $enabled && ! $forceRebuild && ! $recordingGlobal && ! $replayingGlobal) {
+        if (! $enabled && ! $forceRebuild && ! $this->forceRefetch && ! $recordingGlobal && ! $replayingGlobal) {
             return $arguments;
         }
 
         $arguments = $this->popArgument(self::OPTION, $arguments);
         $arguments = $this->popArgument(self::REBUILD_OPTION, $arguments);
+        $arguments = $this->popArgument(self::REFETCH_OPTION, $arguments);
 
         // When `--coverage` is active, piggyback on PHPUnit's CodeCoverage
         // instead of starting our own PCOV / Xdebug session. Running two
@@ -401,6 +425,16 @@ final class Tia implements AddsOutput, HandlesArguments, Terminable
         $graph->replaceEdges($perTest);
         $graph->pruneMissingTests();
 
+        // Fold in the results collected during this same record run. The
+        // `AddsOutput` pass that runs `snapshotTestResults` fires *before*
+        // `terminate()` in the shutdown chain, so by the time the graph
+        // lands on disk, the snapshot pass has already returned empty.
+        // Writing results here means a first `--tia` invocation produces
+        // a graph with edges *and* results — the immediate next run hits
+        // cache for every unchanged test rather than needing a "warm-up"
+        // pass.
+        $this->seedResultsInto($graph);
+
         if (! $this->saveGraph($graph)) {
             $this->output->writeln('  <fg=red>TIA</> failed to write graph.');
             $recorder->reset();
@@ -635,7 +669,7 @@ final class Tia implements AddsOutput, HandlesArguments, Terminable
         // to pull a team-shared baseline so fresh checkouts (new devs, CI
         // containers) don't pay the full record cost. If the pull succeeds
         // the graph is re-read and reconciled against the local env.
-        if (! $graph instanceof Graph && ! $forceRebuild && $this->baselineSync->fetchIfAvailable($projectRoot)) {
+        if (! $graph instanceof Graph && ! $forceRebuild && $this->baselineSync->fetchIfAvailable($projectRoot, $this->forceRefetch)) {
             $graph = $this->loadGraph($projectRoot);
             if ($graph instanceof Graph) {
                 $graph = $this->reconcileFingerprint($graph, $fingerprint);
@@ -1147,6 +1181,31 @@ final class Tia implements AddsOutput, HandlesArguments, Terminable
         $this->saveGraph($graph);
     }
 
+    /**
+     * In-memory equivalent of `snapshotTestResults()` — transfers the
+     * collected results straight into the given graph instance without a
+     * load/save round-trip. Used on the record path where the graph
+     * hasn't hit disk yet and a separate `loadGraph()` would find nothing.
+     */
+    private function seedResultsInto(Graph $graph): void
+    {
+        /** @var ResultCollector $collector */
+        $collector = Container::getInstance()->get(ResultCollector::class);
+
+        foreach ($collector->all() as $testId => $result) {
+            $graph->setResult(
+                $this->branch,
+                $testId,
+                $result['status'],
+                $result['message'],
+                $result['time'],
+                $result['assertions'],
+            );
+        }
+
+        $collector->reset();
+    }
+
     /**
      * Merges per-test status + message from the `ResultCollector` into the
      * TIA graph. Runs after every `--tia` invocation so the graph always has
diff --git a/src/Plugins/Tia/BaselineSync.php b/src/Plugins/Tia/BaselineSync.php
index 97466f85..399bb72e 100644
--- a/src/Plugins/Tia/BaselineSync.php
+++ b/src/Plugins/Tia/BaselineSync.php
@@ -62,6 +62,15 @@ final readonly class BaselineSync
 
     private const string COVERAGE_ASSET = Tia::KEY_COVERAGE_CACHE;
 
+    /**
+     * Cooldown (in seconds) applied after a failed baseline fetch.
+     * Rationale: when the remote workflow hasn't published yet, every
+     * `pest --tia` invocation would otherwise re-hit `gh run list` and
+     * re-print the publish instructions — noisy + slow. Back off for a
+     * day, let the user override with `--tia-refetch`.
+     */
+    private const int FETCH_COOLDOWN_SECONDS = 86400;
+
     public function __construct(
         private State $state,
         private OutputInterface $output,
@@ -72,8 +81,12 @@ final readonly class BaselineSync
      * contents into the TIA state store. Returns true when the graph blob
      * landed; coverage is best-effort since plain `--tia` (no `--coverage`)
      * never reads it.
+     *
+     * `$force = true` (driven by `--tia-refetch`) ignores the post-failure
+     * cooldown so the user can retry on demand without waiting out the
+     * 24h window.
      */
-    public function fetchIfAvailable(string $projectRoot): bool
+    public function fetchIfAvailable(string $projectRoot, bool $force = false): bool
     {
         $repo = $this->detectGitHubRepo($projectRoot);
 
@@ -81,6 +94,16 @@ final readonly class BaselineSync
             return false;
         }
 
+        if (! $force && ($remaining = $this->cooldownRemaining()) !== null) {
+            $this->output->writeln(sprintf(
+                '  <fg=yellow>TIA</> last fetch found no baseline — next auto-retry in %s. '
+                    .'Override with <fg=cyan>--tia-refetch</>.',
+                $this->formatDuration($remaining),
+            ));
+
+            return false;
+        }
+
         $this->output->writeln(sprintf(
             '  <fg=cyan>TIA</> fetching baseline from <fg=white>%s</>…',
             $repo,
@@ -89,6 +112,7 @@ final readonly class BaselineSync
         $payload = $this->download($repo);
 
         if ($payload === null) {
+            $this->startCooldown();
             $this->emitPublishInstructions($repo);
 
             return false;
@@ -102,6 +126,11 @@ final readonly class BaselineSync
             $this->state->write(Tia::KEY_COVERAGE_CACHE, $payload['coverage']);
         }
 
+        // Successful fetch wipes any stale cooldown so the next failure
+        // (say, weeks later) starts a fresh 24h timer rather than inheriting
+        // one from the deep past.
+        $this->clearCooldown();
+
         $this->output->writeln(sprintf(
             '  <fg=green>TIA</> baseline ready (%s).',
             $this->formatSize(strlen($payload['graph']) + strlen($payload['coverage'] ?? '')),
@@ -110,6 +139,54 @@ final readonly class BaselineSync
         return true;
     }
 
+    /**
+     * Seconds left on the cooldown, or `null` when the cooldown is cleared
+     * / expired / unreadable.
+     */
+    private function cooldownRemaining(): ?int
+    {
+        $raw = $this->state->read(Tia::KEY_FETCH_COOLDOWN);
+
+        if ($raw === null) {
+            return null;
+        }
+
+        $decoded = json_decode($raw, true);
+
+        if (! is_array($decoded) || ! isset($decoded['until']) || ! is_int($decoded['until'])) {
+            return null;
+        }
+
+        $remaining = $decoded['until'] - time();
+
+        return $remaining > 0 ? $remaining : null;
+    }
+
+    private function startCooldown(): void
+    {
+        $this->state->write(Tia::KEY_FETCH_COOLDOWN, (string) json_encode([
+            'until' => time() + self::FETCH_COOLDOWN_SECONDS,
+        ]));
+    }
+
+    private function clearCooldown(): void
+    {
+        $this->state->delete(Tia::KEY_FETCH_COOLDOWN);
+    }
+
+    private function formatDuration(int $seconds): string
+    {
+        if ($seconds >= 3600) {
+            return (int) round($seconds / 3600).'h';
+        }
+
+        if ($seconds >= 60) {
+            return (int) round($seconds / 60).'m';
+        }
+
+        return $seconds.'s';
+    }
+
     /**
      * Prints actionable instructions for publishing a first baseline when
      * the consumer-side fetch finds nothing.
diff --git a/src/Support/XdebugGuard.php b/src/Support/XdebugGuard.php
new file mode 100644
index 00000000..539a90ea
--- /dev/null
+++ b/src/Support/XdebugGuard.php
@@ -0,0 +1,179 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Pest\Support;
+
+use Composer\XdebugHandler\XdebugHandler;
+use Pest\Plugins\Tia;
+use Pest\Plugins\Tia\Fingerprint;
+use Pest\Plugins\Tia\Graph;
+
+/**
+ * Re-execs the PHP process without Xdebug on TIA replay runs, matching the
+ * behaviour of composer, phpstan, rector, psalm and pint.
+ *
+ * Xdebug imposes a 30–50% runtime tax on every PHP process that loads it —
+ * even when nothing is actively tracing, profiling or breaking. Plain `pest`
+ * users might rely on Xdebug being loaded (IDE breakpoints, step-through
+ * debugging, custom tooling), so we intentionally leave non-TIA runs alone.
+ *
+ * The guard engages only when ALL of these hold:
+ *   1. `--tia` is present in argv.
+ *   2. No `--tia-rebuild` flag (forced record always drives the coverage
+ *      driver; dropping Xdebug would break the recording).
+ *   3. No `--coverage*` flag (coverage runs need the driver regardless).
+ *   4. A valid graph already exists on disk AND its structural fingerprint
+ *      matches the current environment — i.e. TIA will replay rather than
+ *      record. Record runs need the driver.
+ *   5. Xdebug's configured mode is either empty or exactly `['coverage']`.
+ *      Any other mode (debug, develop, trace, profile, gcstats) signals the
+ *      user wants Xdebug for reasons unrelated to coverage, so we leave it
+ *      alone even on replay.
+ *
+ * `PEST_ALLOW_XDEBUG=1` remains an explicit manual override; it is honoured
+ * natively by `composer/xdebug-handler`.
+ *
+ * @internal
+ */
+final class XdebugGuard
+{
+    /**
+     * Call as early as possible after composer autoload, before any Pest
+     * class beyond the autoloader is touched. Safe when Xdebug is not
+     * loaded (returns immediately) and when `composer/xdebug-handler` is
+     * unavailable (defensive `class_exists` check).
+     */
+    public static function maybeDrop(string $projectRoot): void
+    {
+        if (! class_exists(XdebugHandler::class)) {
+            return;
+        }
+
+        if (! extension_loaded('xdebug')) {
+            return;
+        }
+
+        if (! self::xdebugIsCoverageOnly()) {
+            return;
+        }
+
+        $argv = is_array($_SERVER['argv'] ?? null) ? $_SERVER['argv'] : [];
+
+        if (! self::runLooksDroppable($argv, $projectRoot)) {
+            return;
+        }
+
+        (new XdebugHandler('pest'))->check();
+    }
+
+    /**
+     * True when Xdebug 3+ is running in coverage-only mode (or empty). False
+     * for older Xdebug without `xdebug_info` — be conservative and leave it
+     * loaded; we can't prove the mode is safe to drop.
+     */
+    private static function xdebugIsCoverageOnly(): bool
+    {
+        if (! function_exists('xdebug_info')) {
+            return false;
+        }
+
+        $modes = @xdebug_info('mode');
+
+        if (! is_array($modes)) {
+            return false;
+        }
+
+        $modes = array_values(array_filter($modes, is_string(...)));
+
+        if ($modes === []) {
+            return true;
+        }
+
+        return $modes === ['coverage'];
+    }
+
+    /**
+     * Encodes the argv-based rules: `--tia` must be present, no coverage
+     * flag, no forced rebuild, and TIA must be about to replay rather than
+     * record. Plain `pest` (and anything else without `--tia`) keeps Xdebug
+     * loaded so non-TIA users aren't surprised by behaviour changes.
+     *
+     * @param  array<int, mixed>  $argv
+     */
+    private static function runLooksDroppable(array $argv, string $projectRoot): bool
+    {
+        $hasTia = false;
+
+        foreach ($argv as $value) {
+            if (! is_string($value)) {
+                continue;
+            }
+
+            if ($value === '--coverage'
+                || str_starts_with($value, '--coverage=')
+                || str_starts_with($value, '--coverage-')) {
+                return false;
+            }
+
+            if ($value === '--tia-rebuild') {
+                return false;
+            }
+
+            if ($value === '--tia') {
+                $hasTia = true;
+            }
+        }
+
+        if (! $hasTia) {
+            return false;
+        }
+
+        return self::tiaWillReplay($projectRoot);
+    }
+
+    /**
+     * True when a valid TIA graph already lives on disk AND its structural
+     * fingerprint matches the current environment. Any other outcome
+     * (missing graph, unreadable JSON, structural drift) means TIA will
+     * record and the driver must stay loaded.
+     */
+    private static function tiaWillReplay(string $projectRoot): bool
+    {
+        $path = self::graphPath();
+
+        if (! is_file($path)) {
+            return false;
+        }
+
+        $json = @file_get_contents($path);
+
+        if ($json === false) {
+            return false;
+        }
+
+        $graph = Graph::decode($json, $projectRoot);
+
+        if (! $graph instanceof Graph) {
+            return false;
+        }
+
+        return Fingerprint::structuralMatches(
+            $graph->fingerprint(),
+            Fingerprint::compute($projectRoot),
+        );
+    }
+
+    /**
+     * On-disk location of the TIA graph — mirrors `Bootstrapper::tempDir()`
+     * so both writer and reader stay in sync without a runtime container
+     * lookup (the container isn't booted yet at this point).
+     */
+    private static function graphPath(): string
+    {
+        return dirname(__DIR__, 2)
+            .DIRECTORY_SEPARATOR.'.temp'
+            .DIRECTORY_SEPARATOR.'tia'
+            .DIRECTORY_SEPARATOR.Tia::KEY_GRAPH;
+    }
+}
diff --git a/tests-tia/AffectedSetTest.php b/tests-tia/AffectedSetTest.php
new file mode 100644
index 00000000..288b2227
--- /dev/null
+++ b/tests-tia/AffectedSetTest.php
@@ -0,0 +1,63 @@
+<?php
+
+declare(strict_types=1);
+
+use Pest\TestsTia\Support\Sandbox;
+
+/*
+ * Mutating a source file should narrow replay to the tests that depend
+ * on it. Untouched areas of the suite keep cache-hitting.
+ */
+
+test('editing a source file marks only its dependents as affected', function () {
+    tiaScenario(function (Sandbox $sandbox) {
+        $sandbox->pest(['--tia']);
+
+        $sandbox->write('src/Math.php', <<<'PHP'
+<?php
+
+declare(strict_types=1);
+
+namespace App;
+
+final class Math
+{
+    public static function add(int $a, int $b): int
+    {
+        return $a + $b;
+    }
+
+    public static function sub(int $a, int $b): int
+    {
+        return $a - $b;
+    }
+}
+PHP);
+
+        $process = $sandbox->pest(['--tia']);
+
+        expect($process->isSuccessful())->toBeTrue(tiaOutput($process));
+        expect(tiaOutput($process))->toMatch('/2 affected,\s*1 replayed/');
+    });
+});
+
+test('adding a new test file runs the new test + replays the rest', function () {
+    tiaScenario(function (Sandbox $sandbox) {
+        $sandbox->pest(['--tia']);
+
+        $sandbox->write('tests/ExtraTest.php', <<<'PHP'
+<?php
+
+declare(strict_types=1);
+
+test('extra smoke', function () {
+    expect(true)->toBeTrue();
+});
+PHP);
+
+        $process = $sandbox->pest(['--tia']);
+
+        expect($process->isSuccessful())->toBeTrue(tiaOutput($process));
+        expect(tiaOutput($process))->toMatch('/1 affected,\s*3 replayed/');
+    });
+});
diff --git a/tests-tia/FingerprintDriftTest.php b/tests-tia/FingerprintDriftTest.php
new file mode 100644
index 00000000..b7c5fccb
--- /dev/null
+++ b/tests-tia/FingerprintDriftTest.php
@@ -0,0 +1,52 @@
+<?php
+
+declare(strict_types=1);
+
+use Pest\TestsTia\Support\Sandbox;
+
+/*
+ * Fingerprint splits into structural vs environmental. Hand-forge each
+ * drift flavour on a valid graph and assert the right branch fires.
+ */
+
+test('structural drift discards the graph entirely', function () {
+    tiaScenario(function (Sandbox $sandbox) {
+        $sandbox->pest(['--tia']);
+
+        $graphPath = $sandbox->path().'/vendor/pestphp/pest/.temp/tia/graph.json';
+        $graph = json_decode((string) file_get_contents($graphPath), true);
+        $graph['fingerprint']['structural']['composer_lock'] = str_repeat('0', 32);
+        file_put_contents($graphPath, json_encode($graph));
+
+        $process = $sandbox->pest(['--tia']);
+
+        expect($process->isSuccessful())->toBeTrue(tiaOutput($process));
+        expect(tiaOutput($process))->toContain('graph structure outdated');
+    });
+});
+
+test('environmental drift keeps edges, drops results', function () {
+    tiaScenario(function (Sandbox $sandbox) {
+        $sandbox->pest(['--tia']);
+
+        $graphPath = $sandbox->path().'/vendor/pestphp/pest/.temp/tia/graph.json';
+        $graph = json_decode((string) file_get_contents($graphPath), true);
+
+        $edgeCountBefore = count($graph['edges']);
+
+        $graph['fingerprint']['environmental']['php_minor'] = '7.4';
+        $graph['fingerprint']['environmental']['extensions'] = str_repeat('0', 32);
+        file_put_contents($graphPath, json_encode($graph));
+
+        $process = $sandbox->pest(['--tia']);
+
+        expect($process->isSuccessful())->toBeTrue(tiaOutput($process));
+        expect(tiaOutput($process))->toContain('env differs from baseline');
+        expect(tiaOutput($process))->toContain('results dropped, edges reused');
+
+        $graphAfter = $sandbox->graph();
+        expect(count($graphAfter['edges']))->toBe($edgeCountBefore);
+        expect($graphAfter['fingerprint']['environmental']['php_minor'])
+            ->not()->toBe('7.4');
+    });
+});
diff --git a/tests-tia/Fixtures/sample-project/composer.json b/tests-tia/Fixtures/sample-project/composer.json
new file mode 100644
index 00000000..a72a1f25
--- /dev/null
+++ b/tests-tia/Fixtures/sample-project/composer.json
@@ -0,0 +1,27 @@
+{
+    "name": "pest/tia-sample-project",
+    "type": "project",
+    "description": "Throw-away fixture used by tests-tia to exercise TIA end-to-end.",
+    "require": {
+        "php": "^8.3"
+    },
+    "autoload": {
+        "psr-4": {
+            "App\\": "src/"
+        }
+    },
+    "autoload-dev": {
+        "psr-4": {
+            "Tests\\": "tests/"
+        }
+    },
+    "config": {
+        "sort-packages": true,
+        "allow-plugins": {
+            "pestphp/pest-plugin": true,
+            "php-http/discovery": true
+        }
+    },
+    "minimum-stability": "dev",
+    "prefer-stable": true
+}
diff --git a/tests-tia/Fixtures/sample-project/phpunit.xml b/tests-tia/Fixtures/sample-project/phpunit.xml
new file mode 100644
index 00000000..0c3e5935
--- /dev/null
+++ b/tests-tia/Fixtures/sample-project/phpunit.xml
@@ -0,0 +1,22 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:noNamespaceSchemaLocation="vendor/phpunit/phpunit/phpunit.xsd"
+         bootstrap="vendor/autoload.php"
+         colors="true"
+         cacheDirectory=".phpunit.cache"
+         executionOrder="depends,defects"
+         failOnRisky="false"
+         failOnWarning="false"
+         displayDetailsOnTestsThatTriggerWarnings="true"
+         displayDetailsOnTestsThatTriggerNotices="true">
+    <testsuites>
+        <testsuite name="default">
+            <directory>tests</directory>
+        </testsuite>
+    </testsuites>
+    <source>
+        <include>
+            <directory>src</directory>
+        </include>
+    </source>
+</phpunit>
diff --git a/tests-tia/Fixtures/sample-project/src/Greeter.php b/tests-tia/Fixtures/sample-project/src/Greeter.php
new file mode 100644
index 00000000..e952204e
--- /dev/null
+++ b/tests-tia/Fixtures/sample-project/src/Greeter.php
@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App;
+
+final class Greeter
+{
+    public static function greet(string $name): string
+    {
+        return sprintf('Hello, %s!', $name);
+    }
+}
diff --git a/tests-tia/Fixtures/sample-project/src/Math.php b/tests-tia/Fixtures/sample-project/src/Math.php
new file mode 100644
index 00000000..2f0cafef
--- /dev/null
+++ b/tests-tia/Fixtures/sample-project/src/Math.php
@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App;
+
+final class Math
+{
+    public static function add(int $a, int $b): int
+    {
+        return $a + $b;
+    }
+}
diff --git a/tests-tia/Fixtures/sample-project/tests/GreeterTest.php b/tests-tia/Fixtures/sample-project/tests/GreeterTest.php
new file mode 100644
index 00000000..04131c2c
--- /dev/null
+++ b/tests-tia/Fixtures/sample-project/tests/GreeterTest.php
@@ -0,0 +1,9 @@
+<?php
+
+declare(strict_types=1);
+
+use App\Greeter;
+
+test('greeter greets', function () {
+    expect(Greeter::greet('Nuno'))->toBe('Hello, Nuno!');
+});
diff --git a/tests-tia/Fixtures/sample-project/tests/MathTest.php b/tests-tia/Fixtures/sample-project/tests/MathTest.php
new file mode 100644
index 00000000..609d97ea
--- /dev/null
+++ b/tests-tia/Fixtures/sample-project/tests/MathTest.php
@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+use App\Math;
+
+test('math add', function () {
+    expect(Math::add(2, 3))->toBe(5);
+});
+
+test('math add negative', function () {
+    expect(Math::add(-1, 1))->toBe(0);
+});
diff --git a/tests-tia/Fixtures/sample-project/tests/Pest.php b/tests-tia/Fixtures/sample-project/tests/Pest.php
new file mode 100644
index 00000000..f987b070
--- /dev/null
+++ b/tests-tia/Fixtures/sample-project/tests/Pest.php
@@ -0,0 +1,7 @@
+<?php
+
+declare(strict_types=1);
+
+// Intentionally minimal — tests-tia exercises TIA against the simplest
+// possible Pest harness. Anything more and we end up debugging the
+// fixture instead of the feature under test.
diff --git a/tests-tia/RebuildTest.php b/tests-tia/RebuildTest.php
new file mode 100644
index 00000000..c9d4ecc8
--- /dev/null
+++ b/tests-tia/RebuildTest.php
@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+use Pest\TestsTia\Support\Sandbox;
+
+/*
+ * `--tia-rebuild` short-circuits whatever graph is on disk and records
+ * from scratch. Used when the user knows the cache is wrong.
+ */
+
+test('--tia-rebuild forces record mode even with a valid graph', function () {
+    tiaScenario(function (Sandbox $sandbox) {
+        $sandbox->pest(['--tia']);
+        expect($sandbox->hasGraph())->toBeTrue();
+
+        $graphBefore = $sandbox->graph();
+
+        $process = $sandbox->pest(['--tia', '--tia-rebuild']);
+
+        expect($process->isSuccessful())->toBeTrue(tiaOutput($process));
+        expect(tiaOutput($process))->toContain('recording dependency graph');
+
+        $graphAfter = $sandbox->graph();
+        expect(array_keys($graphAfter['edges']))
+            ->toEqualCanonicalizing(array_keys($graphBefore['edges']));
+    });
+});
diff --git a/tests-tia/RecordReplayTest.php b/tests-tia/RecordReplayTest.php
new file mode 100644
index 00000000..b4498e5a
--- /dev/null
+++ b/tests-tia/RecordReplayTest.php
@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+use Pest\TestsTia\Support\Sandbox;
+
+/*
+ * The canonical cycle:
+ *   1. Cold `--tia` run → record mode → graph written, tests pass.
+ *   2. Subsequent `--tia` runs → replay mode, every test cache-hits.
+ */
+
+test('cold run records the graph', function () {
+    tiaScenario(function (Sandbox $sandbox) {
+        $process = $sandbox->pest(['--tia']);
+
+        expect($process->isSuccessful())->toBeTrue(tiaOutput($process));
+        expect(tiaOutput($process))->toContain('recording dependency graph');
+        expect($sandbox->hasGraph())->toBeTrue();
+
+        $graph = $sandbox->graph();
+        expect($graph)->toHaveKey('edges');
+        expect(array_keys($graph['edges']))->toContain('tests/MathTest.php');
+        expect(array_keys($graph['edges']))->toContain('tests/GreeterTest.php');
+    });
+});
+
+test('warm run replays every test', function () {
+    tiaScenario(function (Sandbox $sandbox) {
+        // Cold pass: records edges AND snapshots results (series mode
+        // runs `snapshotTestResults` in the same `addOutput` pass).
+        $sandbox->pest(['--tia']);
+
+        $process = $sandbox->pest(['--tia']);
+
+        expect($process->isSuccessful())->toBeTrue(tiaOutput($process));
+        // Zero changes → only the `replayed` fragment appears in the
+        // recap; the `affected` fragment is omitted when count is 0.
+        expect(tiaOutput($process))->toMatch('/3 replayed/');
+        expect(tiaOutput($process))->not()->toMatch('/\d+ affected/');
+    });
+});
diff --git a/tests-tia/SourceRevertTest.php b/tests-tia/SourceRevertTest.php
new file mode 100644
index 00000000..c32fb50c
--- /dev/null
+++ b/tests-tia/SourceRevertTest.php
@@ -0,0 +1,46 @@
+<?php
+
+declare(strict_types=1);
+
+use Pest\TestsTia\Support\Sandbox;
+
+/*
+ * Edit a source file, run TIA (tests re-run), revert to the original
+ * bytes, run again — the revert is itself a change vs the previous
+ * snapshot, so the affected tests re-execute rather than replaying the
+ * stale bad-version cache.
+ */
+
+test('reverting a modified file re-triggers its affected tests', function () {
+    tiaScenario(function (Sandbox $sandbox) {
+        $sandbox->pest(['--tia']);
+
+        $original = (string) file_get_contents($sandbox->path().'/src/Math.php');
+
+        $sandbox->write('src/Math.php', <<<'PHP'
+<?php
+
+declare(strict_types=1);
+
+namespace App;
+
+final class Math
+{
+    public static function add(int $a, int $b): int
+    {
+        return 999; // broken
+    }
+}
+PHP);
+
+        $broken = $sandbox->pest(['--tia']);
+        expect($broken->isSuccessful())->toBeFalse();
+
+        $sandbox->write('src/Math.php', $original);
+
+        $recovered = $sandbox->pest(['--tia']);
+
+        expect($recovered->isSuccessful())->toBeTrue(tiaOutput($recovered));
+        expect(tiaOutput($recovered))->toMatch('/2 affected,\s*1 replayed/');
+    });
+});
diff --git a/tests-tia/StatusReplayTest.php b/tests-tia/StatusReplayTest.php
new file mode 100644
index 00000000..d1eb4f0f
--- /dev/null
+++ b/tests-tia/StatusReplayTest.php
@@ -0,0 +1,53 @@
+<?php
+
+declare(strict_types=1);
+
+use Pest\TestsTia\Support\Sandbox;
+
+/*
+ * Cached statuses + assertion counts should survive replay.
+ */
+
+test('assertion counts survive replay', function () {
+    tiaScenario(function (Sandbox $sandbox) {
+        $sandbox->pest(['--tia']);
+
+        $process = $sandbox->pest(['--tia']);
+        $output = tiaOutput($process);
+
+        // MathTest has 2 assertions, GreeterTest has 1 → 3 total.
+        // The "Tests: … (N assertions, … replayed)" banner should show 3.
+        expect($output)->toMatch('/\(3 assertions/');
+    });
+});
+
+test('breaking a test replays as a failure on the next run', function () {
+    tiaScenario(function (Sandbox $sandbox) {
+        // Prime.
+        $sandbox->pest(['--tia']);
+
+        // Break the test. Its test file's edge map still points at
+        // `src/Math.php`; editing the test file counts as a change
+        // and the test re-executes.
+        $sandbox->write('tests/MathTest.php', <<<'PHP'
+<?php
+
+declare(strict_types=1);
+
+use App\Math;
+
+test('math add', function () {
+    expect(Math::add(2, 3))->toBe(999); // wrong
+});
+
+test('math add negative', function () {
+    expect(Math::add(-1, 1))->toBe(0);
+});
+PHP);
+
+        $process = $sandbox->pest(['--tia']);
+
+        expect($process->isSuccessful())->toBeFalse();
+        expect(tiaOutput($process))->toContain('math add');
+    });
+});
diff --git a/tests-tia/Support/Sandbox.php b/tests-tia/Support/Sandbox.php
new file mode 100644
index 00000000..4c3361a2
--- /dev/null
+++ b/tests-tia/Support/Sandbox.php
@@ -0,0 +1,440 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Pest\TestsTia\Support;
+
+use RuntimeException;
+use Symfony\Component\Process\Process;
+
+/**
+ * Throw-away sandbox for a TIA end-to-end scenario.
+ *
+ * On first call in a test run, a shared "template" sandbox is created
+ * under the system temp dir and composer-installed against the host
+ * Pest source. Subsequent `::create()` calls clone the template — cheap
+ * (rcopy + git init) vs. running composer install per test.
+ *
+ * Each test owns its own clone; no cross-test state.
+ *
+ * Set `PEST_TIA_KEEP=1` to skip teardown so a failing scenario can be
+ * reproduced manually — the path is emitted to STDERR.
+ *
+ * @internal
+ */
+final class Sandbox
+{
+    private static ?string $templatePath = null;
+
+    private function __construct(private readonly string $path) {}
+
+    /**
+     * Eagerly provision the shared template. Call once from the harness
+     * bootstrap so parallel workers don't race on first `create()`.
+     */
+    public static function warmTemplate(): void
+    {
+        self::ensureTemplate();
+    }
+
+    public static function create(): self
+    {
+        $template = self::ensureTemplate();
+
+        $path = sys_get_temp_dir()
+            .DIRECTORY_SEPARATOR
+            .'pest-tia-sandbox-'
+            .bin2hex(random_bytes(4));
+
+        self::rcopy($template, $path);
+        self::bootstrapGit($path);
+
+        return new self($path);
+    }
+
+    public function path(): string
+    {
+        return $this->path;
+    }
+
+    public function write(string $relative, string $content): void
+    {
+        $absolute = $this->path.DIRECTORY_SEPARATOR.$relative;
+        $dir = dirname($absolute);
+
+        if (! is_dir($dir) && ! @mkdir($dir, 0755, true) && ! is_dir($dir)) {
+            throw new RuntimeException("Cannot create {$dir}");
+        }
+
+        if (@file_put_contents($absolute, $content) === false) {
+            throw new RuntimeException("Cannot write {$absolute}");
+        }
+    }
+
+    public function delete(string $relative): void
+    {
+        $absolute = $this->path.DIRECTORY_SEPARATOR.$relative;
+
+        if (is_file($absolute)) {
+            @unlink($absolute);
+        }
+    }
+
+    /**
+     * @param  array<int, string>  $flags
+     */
+    public function pest(array $flags = []): Process
+    {
+        // Invoke Pest's bin script through PHP directly rather than the
+        // `vendor/bin/pest` symlink — `rcopy()` loses the `+x` bit when
+        // cloning the template. Going through `php` bypasses the exec
+        // check. Use `PHP_BINARY` (not a bare `php`) so the sandbox
+        // executes under the same interpreter that launched the outer
+        // test suite — otherwise macOS multi-version setups (Herd, brew,
+        // asdf, …) fall back to the first `php` on `$PATH`, which often
+        // lacks the coverage driver TIA's record mode needs.
+        $process = new Process(
+            [PHP_BINARY, 'vendor/pestphp/pest/bin/pest', ...$flags],
+            $this->path,
+            [
+                // Strip any CI signal so TIA doesn't suppress instructions.
+                'GITHUB_ACTIONS' => '',
+                'GITLAB_CI' => '',
+                'CIRCLECI' => '',
+            ],
+        );
+        $process->setTimeout(120.0);
+        $process->run();
+
+        return $process;
+    }
+
+    /**
+     * @return array<string, mixed>|null
+     */
+    public function graph(): ?array
+    {
+        $path = $this->path.'/vendor/pestphp/pest/.temp/tia/graph.json';
+
+        if (! is_file($path)) {
+            return null;
+        }
+
+        $raw = @file_get_contents($path);
+
+        if ($raw === false) {
+            return null;
+        }
+
+        $decoded = json_decode($raw, true);
+
+        return is_array($decoded) ? $decoded : null;
+    }
+
+    public function hasGraph(): bool
+    {
+        return $this->graph() !== null;
+    }
+
+    /**
+     * @param  array<int, string>  $args
+     */
+    public function git(array $args): Process
+    {
+        $process = new Process(['git', ...$args], $this->path);
+        $process->setTimeout(30.0);
+        $process->run();
+
+        return $process;
+    }
+
+    public function destroy(): void
+    {
+        if (getenv('PEST_TIA_KEEP') === '1') {
+            fwrite(STDERR, "[PEST_TIA_KEEP] sandbox: {$this->path}\n");
+
+            return;
+        }
+
+        if (is_dir($this->path)) {
+            self::rrmdir($this->path);
+        }
+    }
+
+    /**
+     * Lazily provisions a once-per-process template with composer already
+     * installed against the host Pest source. Every sandbox clone copies
+     * from here, avoiding a ~30s composer install per test.
+     */
+    private static function ensureTemplate(): string
+    {
+        if (self::$templatePath !== null && is_dir(self::$templatePath.'/vendor')) {
+            return self::$templatePath;
+        }
+
+        // Cache key includes a fingerprint of the host Pest source tree —
+        // when we edit Pest internals, the key changes, old templates
+        // become orphaned, the new template rebuilds. Without this, a
+        // stale template with yesterday's Pest code silently masks today's
+        // code under test.
+        $template = sys_get_temp_dir()
+            .DIRECTORY_SEPARATOR
+            .'pest-tia-template-'
+            .self::hostFingerprint();
+
+        // Serialise template creation across parallel paratest workers.
+        // Without the lock, three workers hitting `ensureTemplate()`
+        // simultaneously each see "no vendor yet → rebuild", stomp on
+        // each other's composer install, and produce half-written
+        // fixtures. `flock` on a sibling lockfile keeps it to one
+        // builder; the others block, then observe the finished
+        // template and skip straight to the fast path.
+        $lockPath = sys_get_temp_dir().DIRECTORY_SEPARATOR.'pest-tia-template.lock';
+        $lock = fopen($lockPath, 'c');
+
+        if ($lock === false) {
+            throw new RuntimeException('Cannot open template lock at '.$lockPath);
+        }
+
+        flock($lock, LOCK_EX);
+
+        try {
+            // Re-check after acquiring the lock — another worker may have
+            // just finished the build while we were waiting.
+            if (is_dir($template.'/vendor')) {
+                self::$templatePath = $template;
+
+                return $template;
+            }
+
+            // Garbage-collect every older template keyed by a different
+            // fingerprint so /tmp doesn't accumulate a 200 MB graveyard
+            // over a month of edits.
+            foreach (glob(sys_get_temp_dir().DIRECTORY_SEPARATOR.'pest-tia-template-*') ?: [] as $orphan) {
+                if ($orphan !== $template) {
+                    self::rrmdir($orphan);
+                }
+            }
+
+            if (is_dir($template)) {
+                self::rrmdir($template);
+            }
+
+            $fixture = __DIR__.'/../Fixtures/sample-project';
+
+            if (! is_dir($fixture)) {
+                throw new RuntimeException('Missing fixture at '.$fixture);
+            }
+
+            if (! @mkdir($template, 0755, true) && ! is_dir($template)) {
+                throw new RuntimeException('Cannot create template at '.$template);
+            }
+
+            self::rcopy($fixture, $template);
+            self::wireHostPest($template);
+            self::composerInstall($template);
+
+            self::$templatePath = $template;
+
+            return $template;
+        } finally {
+            flock($lock, LOCK_UN);
+            fclose($lock);
+        }
+    }
+
+    private static function wireHostPest(string $path): void
+    {
+        $hostRoot = realpath(__DIR__.'/../..');
+
+        if ($hostRoot === false) {
+            throw new RuntimeException('Cannot resolve host Pest root');
+        }
+
+        $composerJson = $path.'/composer.json';
+        $decoded = json_decode((string) file_get_contents($composerJson), true);
+
+        $decoded['repositories'] = [
+            ['type' => 'path', 'url' => $hostRoot, 'options' => ['symlink' => false]],
+        ];
+        $decoded['require']['pestphp/pest'] = '*@dev';
+
+        file_put_contents(
+            $composerJson,
+            json_encode($decoded, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES)."\n",
+        );
+    }
+
+    private static function composerInstall(string $path): void
+    {
+        // Invoke composer via the *same* PHP binary that's running this
+        // process. On macOS multi-version setups (Herd, brew, asdf, etc.)
+        // the `composer` shebang often points at the system PHP, which
+        // may not match the version the test suite booted with — leading
+        // to "your PHP version does not satisfy the requirement" errors
+        // even when the interpreter in use would satisfy it. Going
+        // through `PHP_BINARY` + the located composer binary/phar
+        // sidesteps that entirely.
+        $composer = self::locateComposer();
+        $args = $composer === null
+            ? ['composer', 'install']
+            : [PHP_BINARY, $composer, 'install'];
+
+        $process = new Process(
+            [...$args, '--no-interaction', '--prefer-dist', '--no-progress', '--quiet'],
+            $path,
+        );
+        $process->setTimeout(600.0);
+        $process->run();
+
+        if (! $process->isSuccessful()) {
+            throw new RuntimeException(
+                "composer install failed in template:\n".$process->getOutput().$process->getErrorOutput(),
+            );
+        }
+    }
+
+    /**
+     * Resolves the composer binary to a real path PHP can execute. Returns
+     * `null` when composer isn't findable, in which case the caller falls
+     * back to invoking plain `composer` via `$PATH` (and hopes for the
+     * best — usually fine on CI Linux runners).
+     */
+    private static function locateComposer(): ?string
+    {
+        $probe = new Process(['command', '-v', 'composer']);
+        $probe->run();
+
+        $path = trim($probe->getOutput());
+
+        if ($path === '' || ! is_file($path)) {
+            return null;
+        }
+
+        // `composer` may be a shell-script wrapper (Herd does this) —
+        // resolve the actual phar it invokes. Heuristic: parse out the
+        // last `.phar` argument from the wrapper, fall back to the file
+        // itself if no wrapper is detected.
+        $content = @file_get_contents($path);
+
+        if ($content !== false && preg_match('/\S+\.phar/', $content, $m) === 1) {
+            $phar = $m[0];
+
+            if (is_file($phar)) {
+                return $phar;
+            }
+        }
+
+        return $path;
+    }
+
+    private static function bootstrapGit(string $path): void
+    {
+        // Each clone needs its own repo — TIA's SHA / branch / diff logic
+        // all rely on `.git/`. The template has no git dir so clones start
+        // from a clean slate.
+        $run = function (array $args) use ($path): void {
+            $process = new Process(['git', ...$args], $path);
+            $process->setTimeout(30.0);
+            $process->run();
+
+            if (! $process->isSuccessful()) {
+                throw new RuntimeException('git '.implode(' ', $args).' failed: '.$process->getErrorOutput());
+            }
+        };
+
+        // `.git` may have been cloned from the template if we ever add one
+        // there — nuke it just in case so every sandbox starts fresh.
+        if (is_dir($path.'/.git')) {
+            self::rrmdir($path.'/.git');
+        }
+
+        // Keep `vendor/` and composer lock out of the sandbox's git repo
+        // entirely. With ~thousands of files `git add .` takes tens of
+        // seconds; TIA also ignores vendor paths via `shouldIgnore()` so
+        // tracking them buys nothing except slowness.
+        file_put_contents($path.'/.gitignore', "vendor/\ncomposer.lock\n");
+
+        $run(['init', '-q', '-b', 'main']);
+        $run(['config', 'user.email', 'sandbox@pest.test']);
+        $run(['config', 'user.name', 'Pest Sandbox']);
+        $run(['config', 'commit.gpgsign', 'false']);
+        $run(['add', '.']);
+        $run(['commit', '-q', '-m', 'initial']);
+    }
+
+    /**
+     * Short hash derived from the host Pest source that the template is
+     * built against. Hashing the newest mtime across `src/`, `overrides/`,
+     * and `composer.json` is cheap (one stat each) and catches every edit
+     * that could alter TIA behaviour.
+     */
+    private static function hostFingerprint(): string
+    {
+        $hostRoot = realpath(__DIR__.'/../..');
+
+        if ($hostRoot === false) {
+            return 'unknown';
+        }
+
+        $newest = 0;
+
+        foreach ([$hostRoot.'/src', $hostRoot.'/overrides'] as $dir) {
+            if (! is_dir($dir)) {
+                continue;
+            }
+
+            $iter = new \RecursiveIteratorIterator(
+                new \RecursiveDirectoryIterator($dir, \FilesystemIterator::SKIP_DOTS),
+            );
+
+            foreach ($iter as $file) {
+                if ($file->isFile()) {
+                    $newest = max($newest, $file->getMTime());
+                }
+            }
+        }
+
+        if (is_file($hostRoot.'/composer.json')) {
+            $newest = max($newest, (int) filemtime($hostRoot.'/composer.json'));
+        }
+
+        return substr(sha1($hostRoot.'|'.PHP_VERSION.'|'.$newest), 0, 12);
+    }
+
+    private static function rcopy(string $src, string $dest): void
+    {
+        if (! is_dir($dest) && ! @mkdir($dest, 0755, true) && ! is_dir($dest)) {
+            throw new RuntimeException("Cannot create {$dest}");
+        }
+
+        $iter = new \RecursiveIteratorIterator(
+            new \RecursiveDirectoryIterator($src, \FilesystemIterator::SKIP_DOTS),
+            \RecursiveIteratorIterator::SELF_FIRST,
+        );
+
+        foreach ($iter as $item) {
+            $target = $dest.DIRECTORY_SEPARATOR.$iter->getSubPathname();
+
+            if ($item->isDir()) {
+                @mkdir($target, 0755, true);
+            } else {
+                copy($item->getPathname(), $target);
+            }
+        }
+    }
+
+    private static function rrmdir(string $dir): void
+    {
+        if (! is_dir($dir)) {
+            return;
+        }
+
+        // `rm -rf` shells out but handles symlinks, read-only files, and
+        // the composer-vendor quirks (lock files, .bin symlinks) that
+        // PHP's own recursive delete stumbles on. Non-fatal on failure.
+        $process = new Process(['rm', '-rf', $dir]);
+        $process->setTimeout(60.0);
+        $process->run();
+    }
+}
diff --git a/tests-tia/bootstrap.php b/tests-tia/bootstrap.php
new file mode 100644
index 00000000..65f4ee11
--- /dev/null
+++ b/tests-tia/bootstrap.php
@@ -0,0 +1,65 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * tests-tia bootstrap.
+ *
+ * Pest's automatic `Pest.php` loader scans the configured `testDirectory()`
+ * which defaults to `tests/` and is hard to override from a nested suite.
+ * So instead of relying on `tests-tia/Pest.php` being found, wire the
+ * helpers in via PHPUnit's explicit `bootstrap=` attribute — simpler,
+ * no config-search surprises.
+ */
+require __DIR__.'/../vendor/autoload.php';
+require __DIR__.'/Support/Sandbox.php';
+
+use Pest\TestsTia\Support\Sandbox;
+use Symfony\Component\Process\Process;
+
+// tests-tia exercises the record path end-to-end, which means the
+// sandbox PHP must expose a coverage driver (pcov or xdebug with
+// coverage mode). Without one, `--tia` records zero edges and every
+// scenario assertion fails with a useless "no coverage driver" banner.
+// Bail out loudly at bootstrap so the failure mode is obvious.
+if (! extension_loaded('pcov') && ! extension_loaded('xdebug')) {
+    fwrite(STDERR, "\n");
+    fwrite(STDERR, "  \e[30;43m SKIP \e[0m tests-tia requires a coverage driver (pcov or xdebug).\n");
+    fwrite(STDERR, "         Install one, then retry:  composer test:tia\n\n");
+
+    // Exit 0 so CI doesn't fail when the driver is genuinely absent —
+    // the CI workflow adds pcov explicitly so this branch only fires on
+    // dev machines that haven't set one up.
+    exit(0);
+}
+
+// Pre-warm the shared composer template once, up-front. Without this,
+// parallel workers race on first use — whoever hits `ensureTemplate()`
+// second gets a half-written template. A file-based lock + single
+// bootstrap pre-warm sidesteps the problem entirely.
+Sandbox::warmTemplate();
+
+/**
+ * Runs `$body` inside a fresh sandbox, guaranteeing teardown even when the
+ * body throws. Keeps scenario tests tidy — one line per setup + destroy.
+ */
+function tiaScenario(Closure $body): void
+{
+    $sandbox = Sandbox::create();
+
+    try {
+        $body($sandbox);
+    } finally {
+        $sandbox->destroy();
+    }
+}
+
+/**
+ * Strip ANSI escapes so assertions are terminal-agnostic.
+ */
+function tiaOutput(Process $process): string
+{
+    $output = $process->getOutput().$process->getErrorOutput();
+
+    return preg_replace('/\e\[[0-9;]*m/', '', $output) ?? $output;
+}
diff --git a/tests-tia/phpunit.xml b/tests-tia/phpunit.xml
new file mode 100644
index 00000000..99c042e8
--- /dev/null
+++ b/tests-tia/phpunit.xml
@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:noNamespaceSchemaLocation="../vendor/phpunit/phpunit/phpunit.xsd"
+         bootstrap="bootstrap.php"
+         colors="true"
+         cacheDirectory="../.phpunit.cache/tests-tia"
+         executionOrder="default"
+         failOnRisky="false"
+         failOnWarning="false">
+    <testsuites>
+        <testsuite name="tia">
+            <directory>.</directory>
+            <exclude>Fixtures</exclude>
+            <exclude>Support</exclude>
+        </testsuite>
+    </testsuites>
+</phpunit>