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docs/review-learnings.md

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+<!-- auto-generated by pr-learnings -->
+
+## buildNode.groovy: pnpm must be globally installed before invoking pnpm commands
+
+**Takeaway:** When auto-selecting the install command in `buildNode.groovy` based on lockfile presence, pnpm must be installed globally first (`npm install -g pnpm@<version>`) — emitting `pnpm install --frozen-lockfile` alone will fail in environments where pnpm is not on the PATH.
+
+**Pattern:** Any time `buildNode.groovy` detects a `pnpm-lock.yaml` and constructs an `npm_install_arg` that invokes `pnpm`, the command string must prefix with a global install step. The version should be pinned to avoid silent drift.
+
+**Rationale:** Jenkins agents running Node builds do not have pnpm pre-installed. The auto-selection logic that branches on `fileExists("${repo_name}/pnpm-lock.yaml")` is responsible for producing a self-contained, executable command string — if pnpm is absent from the agent PATH the build fails with a command-not-found error. Reviewers also flagged that lock-file cleanup helpers should cover `pnpm-lock.yaml` alongside `package-lock.json`.
+
+**Concrete example** (from [PR #727](https://github.com/Meesho/devops-lib/pull/727), `src/com/meesho/stages/buildNode.groovy:L193`):
+
+```groovy
+// Before (incomplete — pnpm not guaranteed on PATH)
+if (fileExists("${repo_name}/pnpm-lock.yaml")) {
+    npm_install_arg = 'pnpm install --frozen-lockfile'
+}
+
+// After (reviewer-suggested correction)
+if (fileExists("${repo_name}/pnpm-lock.yaml")) {
+    npm_install_arg = 'npm install -g pnpm@10.33.0 && pnpm install --frozen-lockfile'
+}
+```
+
+**Examples from PRs:**
+- [PR #727](https://github.com/Meesho/devops-lib/pull/727): Auto-selection logic added for pnpm/npm-ci/npm-install; reviewer caught that pnpm must be globally installed first.
+- [PR #728](https://github.com/Meesho/devops-lib/pull/728): Reviewer noted cleanup helpers should also handle `pnpm-lock.yaml`.