Document the develop-leads versioning policy

.github/copilot-instructions.md

@@ -139,6 +139,10 @@ Use: `dotnet test`
 
 ## Commit Guidelines
 
+### Versioning
+
+`develop` leads `main` by a minor. After a `develop -> main` release lands and main's publish completes, bump the minor in [version.json](../version.json) on `develop` via an isolated `bump-version-X.Y` PR, so develop's NBGV prereleases sort above main's last stable. A `develop -> main` promotion that carries only maintenance (dependency bumps, CI/doc fixes, template re-syncs) holds main's version instead — `git checkout main -- version.json` on the promotion branch. See [AGENTS.md "Release Model"](../AGENTS.md#release-model).
+
 ### Pre-Commit Process (Automated by Husky.Net)
 
 The following happens automatically on every commit:

AGENTS.md

@@ -28,6 +28,7 @@ The repo uses a **two-phase model by default**: PRs build fast, publishing is ba
 - **Idempotent weekly republish.** NBGV can produce the same `SemVer2` on an unchanged branch, so the GitHub release step is skipped when the tag already exists, and the NuGet push uses `--skip-duplicate` — an unchanged week is a no-op.
 - **Required check.** The `changes` job is in the `Check pull request workflow status` aggregator's `needs` and **must succeed** (not just "not fail") so a paths-filter error can never let a library-changing PR merge with its smoke build silently skipped. Skipped smoke jobs (no matching change) pass; `failure`/`cancelled` blocks.
 - **Reusable-task parameter contract.** Every `build-*-task.yml` and `build-release-task.yml` takes `ref` (git ref to check out/version), `branch` (logical branch driving config/tags/prerelease — `main` ⇒ Release/non-prerelease, else Debug/prerelease), and where relevant `smoke`. **Branch-derived config keys off `inputs.branch`, never `github.ref_name`** — the publisher's matrix builds `develop` from a run whose `github.ref_name` is `main`. Artifact names are branch-suffixed so both matrix legs coexist in one run.
+- **Versioning is semantic and maintainer-controlled.** The `version` (major.minor) in [`version.json`](./version.json) is the version floor; NBGV appends the git height (the SemVer patch position). `main` builds a stable `X.Y.<height>`; `develop` builds a prerelease `X.Y.<height>-g<sha>`. **`develop` leads `main` by a minor:** after a `develop -> main` release lands and main's publish completes, bump the minor in `version.json` on `develop` in an isolated `bump-version-X.Y` PR, so develop's prereleases sort above main's last stable (at a shared `X.Y`, develop's `X.Y.<height>-g<sha>` sorts *below* main's `X.Y.<height>`). A **maintenance** `develop -> main` promotion (dependency bumps, CI/doc fixes, template re-syncs) holds main's version — `git checkout main -- version.json` on the promotion branch — so `main` advances only its height, not its minor.
 
 ## Build Configuration