# ADR-037: A repo may register more than one technology stack | | | | --- | --- | | **Status** | Accepted | | **Date** | 2026-08-06 | | **Author** | bodurkalukasz | ## Context R20 names one file for the Layer 2 registration: a stack declares what adopting it means in `stack.manifest.json`, "a repo that adopted one carries it", and `self-verify` counts one drift across both layers. `self-verify.mjs` implemented that literally - one filename, read once. Validation case `GATE-12` measured what happens to a repo whose stacks are not one. The worked target was `flutter/flutter`: a Dart framework beside a native engine, permanently, with neither migrating to the other. It could register exactly one. The second stack's entries were not checked, contributed nothing to drift, and - the part that makes this worse than a missing feature - **nothing said a stack had been ignored**. The repo would read `drift 0 - 100% adopted` with half its technology layer unverified. Reproduced on the current tree before anything changed: a fixture carrying `stack.manifest.json` and `stack.dart-flutter.manifest.json` reported only the first, and the second manifest's required entry never appeared in the output at all. The prior round logged this as a contract change rather than fixing it unilaterally, which was the right call: R20 names the filename, and an engine that invents a second convention on its own is how a standard stops meaning one thing. ## Options considered - **A `stacks` array inside one `stack.manifest.json`.** Rejected: the file is authored and shipped by the stack repo, one per technology (ADR-016). A combined file has no owner - every stack would have to know about the others, or the adopting repo would hand-merge two upstream files and own the merge conflict forever. - **A `stacks/` directory of manifests.** Rejected as more structure than the case needs, and it would orphan the single-stack name that every existing adopter carries. - **Leave it and tell a two-stack repo to pick one.** Rejected: it is not a real answer for a repo that genuinely runs both, and the failure mode is silent - the number keeps reporting full adoption of a layer it stopped measuring. - **A namespaced sibling filename.** Chosen. ## Decision A repo carries **one stack manifest per stack it has adopted**, and `self-verify` reads all of them: - `stack.manifest.json` is unchanged and remains the name for a repo with one stack. Nothing an existing adopter carries has to move. - A repo whose stacks coexist adds `stack..manifest.json` per stack. The engine matches `/^stack(?:\.[A-Za-z0-9][A-Za-z0-9._-]*)?\.manifest\.json$/` at the repo root and reads every match **in filename order**, so two runs on one tree report in the same order. - Each file produces its own note naming the file and its `technology`; **the drift number stays one number across every layer**, which is R20's actual promise. - An unparseable stack manifest is drift naming the file. Silence there would reproduce the defect this record exists to fix, one level down. - **Two stacks declaring the same path is reported, not resolved.** The path is checked once per declaration - so it counts twice - and the run names both files. Collapsing them means picking a winner between two upstream repos this one does not own, possibly with different recorded content; saying so and letting the adopter take it upstream is the honest move. ## Consequences - A repo with two permanent stacks can be verified at all, and the number covers both. - The single-stack path is byte-for-byte what it was, which is most adopters. - **Cost accepted:** a duplicated path inflates the denominator slightly. The alternative - a silent collapse - hides a real disagreement between two stack repos, and the warning is cheap to read and rare to see. - **Cost accepted:** the filename now carries meaning (the technology), and nothing checks that it matches the manifest's own `technology` field. A mismatch is cosmetic - both are printed - and a check would fail repos whose stack repo simply named the file differently. - The stack registry (`stacks.json`) is untouched: this is about how an adopting repo records what it adopted, not about what is official. ## Confirmation `GATE-12` is the case. Four cases in `tools/self-verify-drift-test.mjs` hold it in both directions: two stacks both count and are both named; a shared path is checked once per declaration and the doubling is stated; a file that merely resembles the name (`mystack.manifest.json`) is not read as a stack; and an unparseable second manifest is drift rather than a skip. ## What this rules out A repo declaring the same stack twice under two names, and any attempt to reconcile two stacks' claims automatically. The engine reports; the stacks' owners decide. ## Revisit when - The filename-vs-`technology`-field mismatch, accepted here as cosmetic (both are printed, nothing checks they agree), starts causing real confusion rather than staying cosmetic. - The duplicate-path warning (two stacks declaring the same file path, reported but not resolved) proves too noisy in practice, or the standard wants to reconcile two stacks' claims automatically rather than leaving the disagreement to their owners. ## Related - [ADR-016](ADR-016-stacks-are-satellite-repos.md) - one repo per technology, which is why the second registration is a second file rather than a bigger one. - [ADR-022](ADR-022-stacks-linked-not-version-locked.md) - a stack links to the ecosystem rather than to a core version range; unchanged here. - R20 (two layers, one drift number), amended here by one clause.