diff --git a/.changeset/always-install-before-build.md b/.changeset/always-install-before-build.md
new file mode 100644
index 0000000..ba39aa8
--- /dev/null
+++ b/.changeset/always-install-before-build.md
@@ -0,0 +1,7 @@
+---
+"playground-cli": patch
+---
+
+`dot deploy` and `dot build` now run `pnpm install` (or the project's package manager equivalent) before every build, not just when `node_modules/` is missing. A stale `node_modules/` left over from a branch switch or a lockfile bump used to slip past the missing-folder guard and produce opaque Vite/Rollup errors like `"X is not exported by ..."`; the only fix was to re-run `pnpm install` by hand. The install step is idempotent (~1s when nothing has changed), so the happy path is essentially unaffected.
+
+Also surfaces more of the failing build's output in the CLI error message (40 lines instead of 10), so when a build does fail the actual error line — not just the trailing stack trace — makes it into the rendered output. And the same error no longer renders twice in the deploy TUI: the per-section row marks which step failed with `✕`, and the bottom `deploy failed` row carries the message once.
diff --git a/src/commands/deploy/DeployScreen.tsx b/src/commands/deploy/DeployScreen.tsx
index 367bf33..684529f 100644
--- a/src/commands/deploy/DeployScreen.tsx
+++ b/src/commands/deploy/DeployScreen.tsx
@@ -997,7 +997,6 @@ function RunningStage({
                     <Row
                         mark={stepMark(playgroundState.status)}
                         label="publish to playground"
-                        value={playgroundState.error}
                         tone={playgroundState.status === "error" ? "danger" : "muted"}
                     />
                 </Box>
@@ -1030,7 +1029,6 @@ function ContractsSectionView({ state }: { state: ContractsSectionState }) {
             <Row
                 mark={stepMark(state.deployStatus)}
                 label="deploy"
-                value={state.error}
                 tone={state.deployStatus === "error" ? "danger" : "muted"}
             />
             {state.contracts.length > 0 && (
@@ -1072,7 +1070,6 @@ function FrontendSectionView({ state }: { state: FrontendSectionState }) {
             <Row
                 mark={stepMark(state.uploadStatus)}
                 label="upload + dotns"
-                value={state.error}
                 tone={state.uploadStatus === "error" ? "danger" : "muted"}
             />
             {running && state.latestLog && <Hint indent={2}>{truncate(state.latestLog, 120)}</Hint>}
diff --git a/src/utils/build/detect.test.ts b/src/utils/build/detect.test.ts
index a68c0c9..5e08969 100644
--- a/src/utils/build/detect.test.ts
+++ b/src/utils/build/detect.test.ts
@@ -28,7 +28,6 @@ function input(overrides: Partial<DetectInput> = {}): DetectInput {
         packageJson: null,
         lockfiles: new Set(),
         configFiles: new Set(),
-        hasNodeModules: true,
         cargoToml: null,
         ...overrides,
     };
@@ -147,19 +146,23 @@ describe("detectBuildConfig", () => {
 });
 
 describe("detectInstallConfig", () => {
-    it("returns null when node_modules is already present", () => {
+    it("returns an install command even when node_modules already exists (idempotent reconcile)", () => {
+        // A stale node_modules/ — e.g. after a branch switch — bypasses any
+        // missing-folder guard and lets the build run against package versions
+        // that don't match the lockfile. We install unconditionally so that
+        // case can't reach the build step.
         expect(
             detectInstallConfig(
                 input({
                     packageJson: { dependencies: { vite: "^5.0.0" } },
-                    hasNodeModules: true,
+                    lockfiles: new Set(["pnpm-lock.yaml"]),
                 }),
             ),
-        ).toBeNull();
+        ).toEqual({ cmd: "pnpm", args: ["install"], description: "pnpm install" });
     });
 
     it("returns null when package.json is missing", () => {
-        expect(detectInstallConfig(input({ hasNodeModules: false }))).toBeNull();
+        expect(detectInstallConfig(input())).toBeNull();
     });
 
     it("returns null when the project declares no dependencies", () => {
@@ -169,7 +172,6 @@ describe("detectInstallConfig", () => {
             detectInstallConfig(
                 input({
                     packageJson: { scripts: { build: "echo hi" } },
-                    hasNodeModules: false,
                 }),
             ),
         ).toBeNull();
@@ -180,7 +182,6 @@ describe("detectInstallConfig", () => {
             detectInstallConfig(
                 input({
                     packageJson: { devDependencies: { vite: "^7.0.0" } },
-                    hasNodeModules: false,
                 }),
             ),
         ).toEqual({ cmd: "npm", args: ["install"], description: "npm install" });
@@ -192,7 +193,6 @@ describe("detectInstallConfig", () => {
                 input({
                     packageJson: { dependencies: { react: "^19.0.0" } },
                     lockfiles: new Set(["pnpm-lock.yaml"]),
-                    hasNodeModules: false,
                 }),
             ),
         ).toEqual({ cmd: "pnpm", args: ["install"], description: "pnpm install" });
@@ -202,7 +202,6 @@ describe("detectInstallConfig", () => {
                 input({
                     packageJson: { dependencies: { react: "^19.0.0" } },
                     lockfiles: new Set(["bun.lockb"]),
-                    hasNodeModules: false,
                 }),
             ),
         ).toEqual({ cmd: "bun", args: ["install"], description: "bun install" });
@@ -212,7 +211,6 @@ describe("detectInstallConfig", () => {
                 input({
                     packageJson: { dependencies: { react: "^19.0.0" } },
                     lockfiles: new Set(["yarn.lock"]),
-                    hasNodeModules: false,
                 }),
             ),
         ).toEqual({ cmd: "yarn", args: ["install"], description: "yarn install" });
diff --git a/src/utils/build/detect.ts b/src/utils/build/detect.ts
index c39a519..e4c9456 100644
--- a/src/utils/build/detect.ts
+++ b/src/utils/build/detect.ts
@@ -61,8 +61,6 @@ export interface DetectInput {
     lockfiles: Set<string>;
     /** Set of additional config-file basenames (e.g. vite.config.ts). */
     configFiles: Set<string>;
-    /** Whether a node_modules/ directory exists at the project root. */
-    hasNodeModules: boolean;
     /** Raw Cargo.toml contents (used to gate the cdm contract flow). Null when absent. */
     cargoToml: string | null;
 }
@@ -172,17 +170,19 @@ export function detectContractsType(input: DetectInput): ContractsType | null {
 
 /**
  * Decide whether we need to run an install step before building. Returns the
- * install command when the project has dependencies declared but no
- * node_modules/ directory, otherwise null.
+ * install command whenever the project declares any dependencies, otherwise
+ * null.
  *
- * Rationale: without this check, `dot build` for an uninstalled project falls
- * through to `npx vite build` (or similar), which ephemerally downloads the
- * framework binary but can't resolve the project's own `vite.config.ts`
- * imports — yielding a confusing ERR_MODULE_NOT_FOUND deep in the config
- * loader. Auto-installing first eliminates the footgun.
+ * We install unconditionally (not just when node_modules/ is missing) because
+ * a stale node_modules/ — e.g. after a branch switch or a teammate bumping the
+ * lockfile — bypasses the missing-folder guard and lets the build run against
+ * package versions that don't match the lockfile. The resulting "X is not
+ * exported by Y" error from Vite/Rollup is opaque and the user has no signal
+ * that the fix is a re-install. pnpm/yarn/npm are all idempotent when in sync
+ * (~1s no-op), so the cost is negligible. Skipping install for a deps-free
+ * package.json is still safe: there's nothing to install.
  */
 export function detectInstallConfig(input: DetectInput): InstallConfig | null {
-    if (input.hasNodeModules) return null;
     const pkg = input.packageJson;
     if (!pkg) return null;
     const depCount =
diff --git a/src/utils/build/runner.ts b/src/utils/build/runner.ts
index ce1aed4..8d68447 100644
--- a/src/utils/build/runner.ts
+++ b/src/utils/build/runner.ts
@@ -76,7 +76,6 @@ export function loadDetectInput(projectDir: string): DetectInput {
         packageJson,
         lockfiles,
         configFiles,
-        hasNodeModules: existsSync(join(root, "node_modules")),
         cargoToml,
     };
 }
diff --git a/src/utils/deploy/run.test.ts b/src/utils/deploy/run.test.ts
index 577988d..31a367e 100644
--- a/src/utils/deploy/run.test.ts
+++ b/src/utils/deploy/run.test.ts
@@ -62,7 +62,7 @@ const {
         packageJson: { scripts: { build: "vite build" } },
         lockfiles: new Set<string>(),
         configFiles: new Set<string>(),
-        hasNodeModules: true,
+        cargoToml: null,
     })),
     detectContractsTypeMock: vi.fn<() => "foundry" | "hardhat" | "cdm" | null>(() => null),
     runContractsPhaseMock: vi.fn<
diff --git a/src/utils/process.test.ts b/src/utils/process.test.ts
index cb27d3e..53fedc3 100644
--- a/src/utils/process.test.ts
+++ b/src/utils/process.test.ts
@@ -87,9 +87,9 @@ describe("runStreamed", () => {
         ).rejects.toThrow(/\(no output\)/);
     });
 
-    it("caps the captured tail and reports only the LAST 10 lines on failure (not the first)", async () => {
+    it("caps the captured tail and reports only the LAST 40 lines on failure (not the first)", async () => {
         // Generate 60 numbered lines, then exit 1. Tail buffer holds the last
-        // 50; the error message shows the last 10 of those — so 51..60.
+        // 40, which is what the error message reports — so 21..60.
         try {
             await runStreamed({
                 cmd: "/bin/sh",
@@ -99,15 +99,50 @@ describe("runStreamed", () => {
             expect.fail("expected rejection");
         } catch (err) {
             const msg = (err as Error).message;
-            // Last 10 lines must appear.
-            for (let i = 51; i <= 60; i++) {
+            // Last 40 lines must appear.
+            for (let i = 21; i <= 60; i++) {
                 expect(msg).toContain(`line-${i}`);
             }
             // Anything earlier must NOT: confirms we're taking the tail, not
-            // the head, and that the slice is capped at 10.
+            // the head, and that the buffer is capped at 40.
             expect(msg).not.toContain("line-1\n");
-            expect(msg).not.toContain("line-50\n");
-            expect(msg).not.toContain("line-10\n");
+            expect(msg).not.toContain("line-20\n");
+        }
+    });
+
+    it("preserves a Vite/Rollup-style error message that precedes a long stack trace", async () => {
+        // Realistic shape: vite prints the build banner, a single descriptive
+        // error line, a code snippet, and finally a ~12-frame stack trace.
+        // With the older 10-line snippet the actual error was pushed off the
+        // window by the trailing trace; the wider window keeps it visible.
+        const script = [
+            "echo 'vite v7.3.2 building client environment for production...'",
+            "echo 'transforming...'",
+            "echo '✓ 1544 modules transformed.'",
+            "echo '✗ Build failed in 843ms'",
+            "echo 'error during build:'",
+            `echo '  src/utils/contracts.ts (40:9): \"createContractRuntimeFromClient\" is not exported by node_modules/@parity/product-sdk-contracts/dist/index.js'`,
+            "echo 'file: /tmp/contracts.ts:40:9'",
+            "echo '38: import type { PolkadotSigner } from \"polkadot-api\";'",
+            "echo '39: import { keccak256 } from \"@parity/product-sdk-utils\";'",
+            "echo '40: import { createContractRuntimeFromClient } from \"@parity/product-sdk-contracts\";'",
+            "echo '             ^'",
+            "echo '41: import { paseo_asset_hub } from \"@parity/product-sdk-descriptors\";'",
+            "for i in $(seq 1 12); do echo '    at frame-'$i' (file:///.../rollup/dist/es/shared/node-entry.js:1234:5)'; done",
+            "exit 1",
+        ].join("; ");
+
+        try {
+            await runStreamed({
+                cmd: "/bin/sh",
+                args: ["-c", script],
+                description: "vite-like-failure",
+            });
+            expect.fail("expected rejection");
+        } catch (err) {
+            const msg = (err as Error).message;
+            expect(msg).toContain('"createContractRuntimeFromClient" is not exported');
+            expect(msg).toContain("at frame-12");
         }
     });
 });
diff --git a/src/utils/process.ts b/src/utils/process.ts
index a7c0f86..4884dad 100644
--- a/src/utils/process.ts
+++ b/src/utils/process.ts
@@ -34,8 +34,12 @@ export interface RunStreamedOptions {
 
 /**
  * Spawn a child process, stream every non-empty stdout/stderr line through
- * `onData`, and resolve/reject based on exit code. Includes the last ~10
+ * `onData`, and resolve/reject based on exit code. Includes the last ~40
  * lines of output in the rejection message so failures are diagnosable.
+ *
+ * The window is 40 (not 10) because Vite/Rollup and many bundlers print the
+ * meaningful error first and then a 10–20 line stack trace; a smaller window
+ * keeps the trace and drops the message that explains what actually broke.
  */
 export async function runStreamed(opts: RunStreamedOptions): Promise<void> {
     const description = opts.description ?? `${opts.cmd} ${opts.args.join(" ")}`;
@@ -49,7 +53,7 @@ export async function runStreamed(opts: RunStreamedOptions): Promise<void> {
         });
 
         const tail: string[] = [];
-        const MAX_TAIL = 50;
+        const MAX_TAIL = 40;
 
         const forward = (chunk: Buffer) => {
             for (const line of chunk.toString().split("\n")) {
@@ -71,7 +75,7 @@ export async function runStreamed(opts: RunStreamedOptions): Promise<void> {
             if (code === 0) {
                 resolvePromise();
             } else {
-                const snippet = tail.slice(-10).join("\n") || "(no output)";
+                const snippet = tail.join("\n") || "(no output)";
                 rejectPromise(
                     new Error(
                         `${failurePrefix} (${description}) with exit code ${code}.\n${snippet}`,