diff --git a/src/cli/operations/deploy/__tests__/preflight-container.test.ts b/src/cli/operations/deploy/__tests__/preflight-container.test.ts
index 3b203816e..78262a3f8 100644
--- a/src/cli/operations/deploy/__tests__/preflight-container.test.ts
+++ b/src/cli/operations/deploy/__tests__/preflight-container.test.ts
@@ -188,6 +188,19 @@ describe('validateContainerAgents', () => {
     expect(ensureMock).not.toHaveBeenCalled();
   });
 
+  it('does NOT ensure .dockerignore when buildContextPath is set but the Dockerfile is missing (ordering guard)', () => {
+    // Dockerfile missing — ensure must be SKIPPED (runs only after validation), so a failing deploy
+    // leaves no stray .dockerignore and the friendly "Dockerfile not found" error is not masked.
+    mockedExistsSync.mockReturnValue(false);
+
+    const spec = makeSpec([
+      { name: 'mono', build: 'Container', codeLocation: dir('agents/mono'), buildContextPath: dir('.') },
+    ]);
+
+    expect(() => validateContainerAgents(spec, CONFIG_ROOT)).toThrow(/Dockerfile not found/);
+    expect(ensureMock).not.toHaveBeenCalled();
+  });
+
   it('warns when Dockerfile uses deprecated bookworm base image', () => {
     mockedExistsSync.mockReturnValue(true);
     mockedReadFileSync.mockReturnValue(
diff --git a/src/cli/operations/deploy/preflight.ts b/src/cli/operations/deploy/preflight.ts
index ca7281c46..5bf91d434 100644
--- a/src/cli/operations/deploy/preflight.ts
+++ b/src/cli/operations/deploy/preflight.ts
@@ -212,22 +212,23 @@ export function validateContainerAgents(projectSpec: AgentCoreProjectSpec, confi
         errors.push(
           `Agent "${agent.name}": ${agent.dockerfile ?? DOCKERFILE_NAME} not found at ${dockerfilePath}. Container agents require a Dockerfile.`
         );
-      }
-      warnDeprecatedBaseImage(dockerfilePath, agent.name);
-
-      // Dockerfile validated. buildContextPath widens the docker build context (e.g. the whole repo);
-      // ensure a .dockerignore at that root so secrets/junk (.env, .git, agentcore/) are never baked
-      // into the local image. Both local and deploy honor this file; it is created only when absent
-      // (never overwrites the user's) and only AFTER validation — so a failing deploy leaves no stray
-      // file and this never masks the friendly "Dockerfile not found" error above.
-      if (agent.buildContextPath) {
-        const created = ensureBuildContextDockerignore(buildContext);
-        if (created) {
-          console.warn(
-            `Agent "${agent.name}": created ${created} with default secret exclusions because buildContextPath is ` +
-              `set (the entire context is sent to Docker/CodeBuild). Review and commit it; edit to include any ` +
-              `intentionally-bundled files.`
-          );
+      } else {
+        warnDeprecatedBaseImage(dockerfilePath, agent.name);
+
+        // Dockerfile validated. buildContextPath widens the docker build context (e.g. the whole repo);
+        // ensure a .dockerignore at that root so secrets/junk (.env, .git, agentcore/) are never baked
+        // into the local image. Both local and deploy honor this file; it is created only when absent
+        // (never overwrites the user's) and only AFTER validation — so a failing deploy leaves no stray
+        // file and this never masks the friendly "Dockerfile not found" error above.
+        if (agent.buildContextPath) {
+          const created = ensureBuildContextDockerignore(buildContext);
+          if (created) {
+            console.warn(
+              `Agent "${agent.name}": created ${created} with default secret exclusions because buildContextPath is ` +
+                `set (the entire context is sent to Docker/CodeBuild). Review and commit it; edit to include any ` +
+                `intentionally-bundled files.`
+            );
+          }
         }
       }
     }
diff --git a/src/schema/schemas/__tests__/agent-env.test.ts b/src/schema/schemas/__tests__/agent-env.test.ts
index 750f1a0d0..076ec581a 100644
--- a/src/schema/schemas/__tests__/agent-env.test.ts
+++ b/src/schema/schemas/__tests__/agent-env.test.ts
@@ -566,6 +566,14 @@ describe('AgentEnvSpecSchema - dockerfile', () => {
       true
     );
   });
+
+  it('rejects "." (names the build-context directory itself → broken `docker build -f .`)', () => {
+    expect(AgentEnvSpecSchema.safeParse({ ...validContainerAgent, dockerfile: '.' }).success).toBe(false);
+  });
+
+  it('accepts a "./"-prefixed filename (normalizes to the file)', () => {
+    expect(AgentEnvSpecSchema.safeParse({ ...validContainerAgent, dockerfile: './Dockerfile' }).success).toBe(true);
+  });
 });
 
 describe('AgentEnvSpecSchema - buildContextPath', () => {
@@ -663,6 +671,13 @@ describe('AgentEnvSpecSchema - customDockerBuildArgs', () => {
     ).toBe(false);
   });
 
+  it('rejects a build-arg key over 255 characters (env-var-name length limit via EnvVarNameSchema)', () => {
+    const longKey = 'A' + 'B'.repeat(255); // 256 chars
+    expect(
+      AgentEnvSpecSchema.safeParse({ ...validContainerAgent, customDockerBuildArgs: { [longKey]: 'v' } }).success
+    ).toBe(false);
+  });
+
   it.each([
     'IMAGE_URI',
     'ECR_REGISTRY',
diff --git a/src/schema/schemas/agent-env.ts b/src/schema/schemas/agent-env.ts
index dc286134a..2a806be8f 100644
--- a/src/schema/schemas/agent-env.ts
+++ b/src/schema/schemas/agent-env.ts
@@ -101,7 +101,9 @@ const DOCKERFILE_PATH_ALLOWED_CHARS = /^[A-Za-z0-9._/-]+$/;
 
 /**
  * True when `p` is a safe relative Dockerfile path within the build context: allowed chars only, no
- * leading slash (absolute), and no empty ('' from a leading/trailing/double slash) or '..' segments.
+ * leading slash (absolute), no empty ('' from a leading/trailing/double slash) or '..' segments, and
+ * it must name a file — not the build-context directory itself (a value like '.' or './' resolves to
+ * the context dir, producing a broken `docker build -f <dir>`).
  *
  * The single source of truth shared by `DockerfilePathSchema` (config-validation time) and the runtime
  * `getDockerfilePath` guard, so the two can never diverge — e.g. one accepting '.docker/Dockerfile'
@@ -110,7 +112,10 @@ const DOCKERFILE_PATH_ALLOWED_CHARS = /^[A-Za-z0-9._/-]+$/;
 export function isValidDockerfilePath(p: string): boolean {
   if (!DOCKERFILE_PATH_ALLOWED_CHARS.test(p)) return false;
   if (p.startsWith('/')) return false;
-  return !p.split('/').some(segment => segment === '' || segment === '..');
+  const segments = p.split('/');
+  if (segments.some(segment => segment === '' || segment === '..')) return false;
+  // Must resolve to a file inside the context, not the context dir: reject '.', './', '././', etc.
+  return segments.some(segment => segment !== '.');
 }
 
 /**