feat(pgpm-core): rebundleWorkspace — emit chunks as separate modules with control-only cross-chunk deps

[pyramation]

Summary

Atom 4, third slice: the "modular workspace" carve. Where rebundleModule (#1412) collapses a module into fewer changes within one extension, rebundleWorkspace emits each chunk as its own tiny module — the same monolith sliced into independently publishable forks (a users module, an admin module, …). This is where the control-only cross-chunk dep mode from deep-dive-4 finally has a home: cross-module ordering rides on the control-file requires, not on plan cross-references.

The emitted directory is a real, discoverable, deployable pgpm workspace, via two new reusable helpers in workspace/minimal.ts:

writeMinimalWorkspace(dir)   → pgpm.json  { "packages": ["packages/*"] }   # workspace marker getWorkspacePath walks up to
writeMinimalModule(dir, ...) → pgpm.plan, <name>.control, Makefile, package.json, deploy|revert|verify/<change>.sql

writeMinimalModule emits the minimal file set pgpm needs — matching what pgpm init scaffolds, minus the network-fetched boilerplate (README/LICENSE/jest/tests/lint configs). The .control carries the full extension shape (comment, default_version, module_pathname, requires, relocatable, superuser), and the Makefile is standard PGXS. These are generic scaffolding knives, usable by any emitter — not rebundle-specific.

rebundleWorkspace composition:

rebundleWorkspace(sourceDir, { outputDir, crossChunkDepMode }) →
  outputDir/
    pgpm.json
    packages/<chunk>/  (one per chunk, via writeMinimalModule; merged deploy/revert/verify via mergeChunkScript)

crossChunkDepMode (default control-only):

• control-only — deps live only in control requires; the plan change has no cross-ref. Extension install/deploy ordering handles the rest — the right shape for versioned module forks.
• change — additionally records the fine-grained plan cross-ref (<dep>:<dep>).

Reuses existing plumbing throughout: rebundlePlan (chunk model + deploy order), the extracted mergeChunkScript/mergeSqlStatements (shared with rebundleModule/packageModule), and slice's generatePlanContent. Tags are remapped onto their sealing chunk-module.

Gates.

1. Byte-identical: workspace deploy (all package deploy scripts concatenated in deploy order) and the original module deploy both go through the same mergeSqlStatements pipeline; equality proves the carve preserved the deployed statements and their order.
2. Actually deploys: a new integration test deploys the emitted workspace module-by-module in deploy order against Postgres and asserts the schemas/tables exist and one merged change per chunk is recorded.

Purely additive — new rebundleWorkspace + crossChunkDepMode + the workspace/minimal helpers; rebundleModule/rebundlePlan and every existing packaging/slice path are untouched.

Test plan

• 8 rebundleWorkspace tests (real DDL, no DB): per-chunk module layout + pgpm.json/Makefile, control-only vs change dep representation, no-dep root module, tag remap, byte-identical gate in both dep modes + overwrite guard.
• New workspace/minimal unit tests: pgpm.json discoverable via pgpmPath, module discoverable via modulePath, full control fields, PGXS Makefile, missing-script/non-empty guards.
• New deploy-integration test: emitted control-only workspace deploys via PgpmMigrate.deploy in deploy order; auth/billing schemas + tables created; 2 merged changes recorded.
• Full @pgpmjs/core suite green with Postgres up: 435/435 (66 suites). tsc --noEmit and pnpm build clean.

Link to Devin session: https://app.devin.ai/sessions/ad40d16f38a349b48eb7ce9375e27e6e
Requested by: @pyramation

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