Add testable task descriptions: T0.1 through T0.9

Each task includes:
- Scope: what to build
- Implementation: code sketches + details
- Verification: concrete test criteria
- Done criteria: acceptance checklist

tasks/T0.4.md

@@ -0,0 +1,72 @@
+# T0.4: Pi & Error Classification
+
+## Scope
+Implement `action/skills.go` with `PrepareSkillsActivity` and `classifyPiErr` for skill prep via homelab API.
+
+## Implementation
+
+### File: `action/skills.go`
+```go
+type SkillRef struct {
+    Name string
+    URL  string
+}
+
+type PrepareSkillsInput struct {
+    Skills        []SkillRef
+    StreamTimeout time.Duration
+}
+
+func PrepareSkillsActivity(ctx context.Context, in PrepareSkillsInput) error
+    // For each skill, run: pi clone-or-fetch $skill.URL
+    // Pass --stream-timeout=$StreamTimeout to pi
+    // Each skill behind its own lock (not orchestrator.lock)
+    // On error, return classified error (see below)
+
+func classifyPiErr(err error) error
+    // 4xx (400-499): NonRetryableApplicationError "PiClientError"
+    // 504: ApplicationError "PiStreamTimeout"
+    // 5xx (500-599, except 504): leave retryable
+    // Other network errors: leave retryable
+```
+
+## Error Buckets
+
+### Bucket 1: 4xx (PiClientError)
+- Status code 400-499
+- Non-retryable: bad request, auth error, not found
+- Temporal stops retrying immediately
+- Activity fails
+
+### Bucket 2: 5xx except 504 (generic 5xx)
+- Status code 500-503, 505-599
+- Retryable: server error, likely transient
+- Temporal backs off + retries until `ScheduleToCloseTimeout` (5m)
+
+### Bucket 3: 504 (PiStreamTimeout)
+- Status code 504
+- Means pi's SSE stream-read timed out
+- Retryable, BUT: Orchestrator doubles `config.Tuning.PiRetry.StreamTimeout` before retry
+- Next attempt uses wider timeout
+
+## Verification
+```bash
+cd /Users/rockliang/workplace/Poimen/workflows
+go test -v ./tests -run TestPiErrors
+
+# Test file: tests/pi_test.go
+```
+
+Test cases:
+- Mock 400 response → NonRetryableApplicationError returned
+- Mock 403 response → NonRetryableApplicationError returned
+- Mock 500 response → retryable error returned
+- Mock 503 response → retryable error returned
+- Mock 504 response → ApplicationError type "PiStreamTimeout" returned
+- Mock network timeout → retryable error returned
+
+## Done Criteria
+- `go test ./tests -run TestPiErrors` passes all 6 test cases
+- All error buckets correctly classified
+- No panics on nil pointers
+- Error messages include HTTP status code