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+<!-- m-wiki: type=concept slug=config-only-detection topic=build base-sha=28f54cf7bef9 generated-at=2026-05-12T00:00:00+00:00 sources=[] -->
+
+> Generated 2026-05-12 at base-sha 28f54cf7bef9. Type: concept. 0 sources.
+
+# Config-Only Change Detection
+
+When a commit only changes YAML config files (no source code), each language builder skips the compile/test/image-build steps and instead fetches the last-built image tag from GAR (Google Artifact Registry). This avoids rebuilding identical binaries when only configs changed.
+
+## Where it applies in this repo
+
+Implemented independently in each language builder (`src/com/meesho/stages/buildMaven.groovy`, `buildGo.groovy`, `buildNode.groovy`, etc.).
+
+The detection pattern varies slightly by builder but follows the same logic:
+
+1. Run `git diff HEAD~1 -- configs/` (or `git diff ORIG_HEAD -- configs/`).
+2. If the diff is non-empty AND no source files changed → set `appConfigChanges = true`, skip compilation.
+3. Fetch the latest image tag from the artifact bucket (S3 or GCS) or GAR.
+4. Set `env.TAG` to the fetched tag.
+5. Proceed directly to `deployArgoCD.run()`.
+
+The check is gated by `skip_s3_check` in `config.yaml`. Setting `skip_s3_check: true` forces a full rebuild even when only configs changed.
+
+## Why this design
+
+Config-only deployments are common at Meesho (dynamic config updates, feature flags). Rebuilding the entire Java or Go binary for a one-line YAML change wastes 3–10 minutes. By reusing the last image tag and skipping straight to ArgoCD deploy, the pipeline completes in ~1 minute for config-only changes.
+
+The detection relies on `git diff` against the previous commit, so it only works when the commit history is linear. Force-pushes or squash merges may produce false negatives (full rebuild triggered unnecessarily).
+
+## Related
+
+- [Language builds](../07-LANGUAGE-BUILDS.md) — where this check is embedded per builder
+- [Build dispatch](build-dispatch.md) — the builder instance that contains this check
+
+## Sources
+
+(no raw/ sources at bootstrap)
+
+## Notes
+
+<!-- Anything below is human-owned. wiki-init never reads or modifies content under this heading. -->
+
+---
+
+[← Wiki index](../../index.md)
+
+<!-- atomic: keep this page ≤600 words. New scope → new concept page that builds on this one. Do not append paragraphs here. -->