feat: add us-cpa tax-year source corpus

docs/us-cpa.md

@@ -4,7 +4,14 @@
 
 ## Current Milestone
 
-Milestone 1 provides the initial package, CLI surface, skill wrapper, and test harness. Tax logic, IRS corpus download, case workflows, rendering, and review logic are not implemented yet.
+Milestone 2 now adds the first tax-year corpus layer:
+
+- deterministic cache layout under `~/.cache/us-cpa` by default
+- `fetch-year` download flow for the bootstrap IRS corpus
+- source manifest with URL, hash, authority rank, and local path traceability
+- authority ranking hooks for IRS materials and future primary-law escalation
+
+Tax logic, case workflows, rendering, and review logic are still pending.
 
 ## CLI Surface
 
@@ -18,6 +25,27 @@ skills/us-cpa/scripts/us-cpa render-forms --tax-year 2025 --case-dir ~/tax-cases
 skills/us-cpa/scripts/us-cpa export-efile-ready --tax-year 2025 --case-dir ~/tax-cases/2025-jane-doe
 ```
 
+## Tax-Year Cache
+
+Default cache root:
+
+```text
+~/.cache/us-cpa
+```
+
+Override for isolated runs:
+
+```bash
+US_CPA_CACHE_DIR=/tmp/us-cpa-cache skills/us-cpa/scripts/us-cpa fetch-year --tax-year 2025
+```
+
+Current `fetch-year` bootstrap corpus for tax year `2025` is verified against live IRS `irs-prior` PDFs for:
+
+- Form 1040
+- Schedules 1, 2, 3, A, B, C, D, SE, and 8812
+- Form 8949
+- General Form 1040 instructions and selected schedule/form instructions
+
 ## Interaction Model
 
 - `question`
@@ -47,10 +75,25 @@ skills/us-cpa/scripts/us-cpa export-efile-ready --tax-year 2025 --case-dir ~/tax
 
 - JSON by default
 - markdown available with `--format markdown`
-- current milestone responses are scaffold payloads with `status: "not_implemented"`
+- `question`, `prepare`, `review`, `extract-docs`, `render-forms`, and `export-efile-ready` still emit scaffold payloads with `status: "not_implemented"`
+- `fetch-year` emits a downloaded manifest location and source count
 
 ## Scope Rules
 
 - U.S. federal individual returns only in v1
 - official IRS artifacts are the target output for compiled forms
 - conflicting facts must stop the workflow for user resolution
+
+## Authority Ranking
+
+Current authority classes are ranked to preserve source hierarchy:
+
+- IRS forms
+- IRS instructions
+- IRS publications
+- IRS FAQs
+- Internal Revenue Code
+- Treasury regulations
+- other primary authority
+
+Later research and review flows should consume this ranking rather than inventing their own.