docs(designs): place subprocess runner under tests/regression

Move PR 2's subprocess-driven tier from tests/integration/golden_templates/
to tests/regression/golden_templates/. Aligns with the existing
tests/regression/deploy/ and tests/regression/package/ suites — same
shape (real `sam` subprocess, real AWS credentials, daily-only).

Bonus: integration-tests.yml's existing other-and-e2e matrix entry
already collects tests/regression/, so no new matrix entry or workflow
edit is needed for the regression tier to start running.

Renamed "integration tier" → "regression tier" throughout for clarity.

Author: bnusunny

designs/golden_templates_and_semver_check.md

@@ -28,11 +28,15 @@ requires a major-version bump whenever a pin changes.
 What will be changed?
 ---------------------
 
-Add a new `tests/golden/` corpus and harness, a new daily integration tier
-under `tests/integration/golden_templates/`, and a tiny standalone GitHub
-workflow that enforces the semver rule. The corpus covers both LE and
-non-LE templates across four axes: SAM resources, packageable CFN resources,
-LE intrinsics, and cross-cutting features.
+Add a new `tests/golden/` corpus and harness (per-PR unit tier), a daily
+subprocess-driven tier under `tests/regression/golden_templates/`, and a
+tiny standalone GitHub workflow that enforces the semver rule. The corpus
+covers both LE and non-LE templates across four axes: SAM resources,
+packageable CFN resources, LE intrinsics, and cross-cutting features.
+
+The two tiers share `tests/golden/templates/` as their single corpus
+source — the regression tier reads case directories straight from the
+unit tier so authoring a new case lands in both places at once.
 
 Success criteria for the change
 -------------------------------
@@ -53,7 +57,7 @@ Success criteria for the change
 Out-of-Scope
 ------------
 
-- No deploy step. The integration tier stops at packaged-template output
+- No deploy step. The regression tier stops at packaged-template output
   — no CloudFormation, no real Lambdas.
 - No CFN compatibility check (e.g. `cfn-lint`, `ValidateTemplate`) at this
   stage. The corpus pins what *SAM-CLI* produces; CFN-side parity is a
@@ -139,14 +143,19 @@ tests/golden/                                   # NEW
     ├── language_extensions/<case>/...          # LE axis
     └── cross_cutting/<case>/...                # nested stacks, AWS::Include, etc.
 
-tests/integration/golden_templates/             # NEW
+tests/regression/golden_templates/              # NEW
 ├── test_golden_subprocess.py                   # imports tests/golden/templates as data
 └── structural_compare.py                       # looser comparator for real-CLI output
 ```
 
 The `tests/golden/templates/` directory is the single source of truth for
-the corpus. Both the unit tier (`tests/golden/`) and the integration tier
-(`tests/integration/golden_templates/`) read from it; nothing is duplicated.
+the corpus. Both the unit tier (`tests/golden/`) and the regression tier
+(`tests/regression/golden_templates/`) read from it; nothing is duplicated.
+
+The regression tier sits alongside the existing `tests/regression/deploy/`
+and `tests/regression/package/` suites — they're structurally similar:
+real `sam` subprocess invocation, real AWS credentials via the
+integration-tests workflow's OIDC role, daily-only execution.
 
 ### Per-case directory layout
 
@@ -197,7 +206,7 @@ no `boto3` stubbing.
 - Single trailing newline.
 
 The harness invokes the same high-level functions the CLI invokes; it does
-not re-implement the pipeline. The integration tier verifies that contract
+not re-implement the pipeline. The regression tier verifies that contract
 holds.
 
 ### Pytest collection
@@ -311,10 +320,17 @@ estimated <30s for ~50 cases. The existing Windows `TEMP=D:\Temp` shim
 already handles temp-dir contention. No new workflow file (the semver gate
 above is its own workflow, but the corpus tests ride on `build.yml`).
 
-### Integration tier
+### Regression tier
+
+Daily run on the existing `integration-tests.yml` workflow. The
+workflow's `other-and-e2e` matrix entry already collects
+`tests/regression/`, so adding `tests/regression/golden_templates/` is
+picked up automatically — **no new matrix entry, no workflow edit**. The
+suite sits alongside the existing `tests/regression/deploy/` and
+`tests/regression/package/` directories, which have the same shape (real
+`sam` subprocess + real AWS credentials, daily-only).
 
-Daily run on the existing `integration-tests.yml` matrix (one new entry:
-`golden-templates`). Per case:
+Per case:
 
 1. Copy case dir to a temp working dir; copy `src/`.
 2. `sam build [--language-extensions]` subprocess; assert exit 0; read
@@ -331,7 +347,7 @@ Daily run on the existing `integration-tests.yml` matrix (one new entry:
      dict-vs-string differences (the #9029 bug class).
 
 The comparator lives in
-`tests/integration/golden_templates/structural_compare.py` and is reused
+`tests/regression/golden_templates/structural_compare.py` and is reused
 for both build and package outputs.
 
 #### Why structural, not byte-exact
@@ -343,7 +359,7 @@ output) or constant churn from environmental noise. Structural comparison
 answers "did the user-visible output shape change?" — which is what catches
 the four bugs we just fixed.
 
-If the unit tier passes but the integration tier fails for a case, the
+If the unit tier passes but the regression tier fails for a case, the
 in-process harness has drifted from the CLI surface — investigation, not
 a re-pin.
 
@@ -353,7 +369,9 @@ Each PR is independently reviewable; LOC estimates are upper-bound net diff.
 
 - **PR 0** (this design doc).
 - **PR 1** — Harness skeleton, three sentinel cases, semver gate workflow.
-- **PR 2** — Integration runner.
+- **PR 2** — Regression-tier subprocess runner under
+  `tests/regression/golden_templates/`. Picked up by the existing
+  `other-and-e2e` matrix entry — no workflow edit required.
 - **PR 3** — SAM resources axis: Function variants (~10 cases).
 - **PR 4** — SAM resources axis: Api / HttpApi / StateMachine / others
   (~10 cases).
@@ -386,7 +404,7 @@ Security Considerations
 -----------------------
 
 The harness intentionally invokes only in-process SAM-CLI code; no
-network calls, no credentials, no AWS API access. The integration tier
+network calls, no credentials, no AWS API access. The regression tier
 uses the existing integration-tests workflow's IAM role and S3 bucket;
 no new permissions required.
 
@@ -405,7 +423,7 @@ Subprocess-only harness (no in-process)
 Every golden runs the real `sam` CLI as a subprocess. Rejected: process
 startup × N templates is too slow for a per-PR gate; flakier on Windows;
 deterministic package output without `moto` is hard. Subprocess invocation
-is kept, but only at the daily integration tier where speed and
+is kept, but only at the daily regression tier where speed and
 determinism matter less.
 
 Snapshot plugin (`syrupy`, `pytest-snapshot`)