Route monorepo TagBot to the registered package

[ChrisRackauckas-Claude]

Summary

• add a reusable monorepo TagBot dispatcher that resolves JuliaTagBot's General registry PR to one root or lib/* package
• keep retry comments and untargeted manual runs as serialized full audits
• deduplicate concurrent runs per package and retain the deprecated lookback input without forwarding it
• document the new caller and test target resolution

Root cause

The previous monorepo convention started TagBot once for the root and once for every registered subpackage on every JuliaTagBot comment. OrdinaryDiffEq currently expands one registration into 57 jobs. A burst of 18 registry merges expanded into 1,026 jobs, exhausted the shared GitHub API allowance, and caused 403 responses followed by long TagBot backoffs.

Implementation

The resolver extracts the JuliaRegistries/General PR number from the bot comment, reads the standardized New version: Package vX.Y.Z title, and validates the name against the caller's root and lib/*/Project.toml files. The resulting one-element matrix invokes the existing tagbot.yml reusable workflow only for that package.

JuliaTagBot retry comments without a General PR link and manual dispatches without a package intentionally discover every package, but use max-parallel: 1. Manual dispatch can name one package. Runs for the same subdirectory share a non-cancelling concurrency group.

The existing lookback workflow input remains accepted for v1 compatibility but is documented as ignored and is no longer forwarded. TagBot itself deprecated the setting and checks all registered versions.

Validation

• python3 -m unittest discover -s test -p 'test_resolve_monorepo_tagbot.py' -v — 9 tests passed
• julia --color=yes test/runtests.jl — all existing testsets passed
• actionlint -color .github/workflows/*.yml — passed with no output
• Runic v1.7.0 --check scripts test/runtests.jl — passed with no output
• live resolver check using General PR 160472 and the OrdinaryDiffEq checkout — resolved only lib/OrdinaryDiffEqBDF, package OrdinaryDiffEqBDF, version 2.3.0

This adds a public reusable workflow and should be released as a backward-compatible minor v1 release before dependent caller PRs merge.

Ignore this PR until reviewed by @ChrisRackauckas.

[ChrisRackauckas-Claude]

Plan / scratchpad:

1. Validate the resolver against root, subpackage, retry, manual, and invalid-package cases.
2. Keep the existing single-package workflow compatible while adding targeted monorepo routing.
3. Confirm actionlint, the repository Julia tests, Runic, and a live General PR lookup locally.
4. Stack an OrdinaryDiffEq caller PR on this workflow; it must wait for this PR to merge and for the moving v1 tag to include the release.
5. Monitor CI on both drafts and record any follow-up commits here.

The upstream TagBot Action still scans all historical versions for the selected package because it has no exact-version Action input. This PR removes the 57-package fan-out without depending on TagBot internals.

[ChrisRackauckas-Claude]

Follow-up d043414 documents and preserves the caller permission block. GitHub reusable workflows can only maintain or reduce the caller token permissions, so the central workflow cannot elevate a read-only caller to contents: write. Local follow-up validation: git diff --check and actionlint both pass.

[ChrisRackauckas-Claude]

The dependent OrdinaryDiffEq caller draft is now open: SciML/OrdinaryDiffEq.jl#3866. It must remain blocked until this PR merges and the moving v1 tag includes the new workflow/action.