Project 20: Freemium Plugin With License Activation

A freemium plugin with feature gates, license activation, offline grace mode, and revocation handling.

Quick Reference

Attribute Value
Difficulty Level 5
Time Estimate 24-42h
Main Programming Language TypeScript
Alternative Programming Languages JavaScript, Go, Node + SQL
Coolness Level Level 5 (Product + backend integration)
Business Potential Level 5 (Revenue engine)
Prerequisites Entitlement matrix modeling, License token verification, Webhook consistency and idempotency
Key Topics Licensing, entitlement, subscription integration

1. Learning Objectives

By completing this project, you will:

  1. Build a production-quality implementation of Freemium Plugin With License Activation.
  2. Apply concept boundaries around Entitlement matrix modeling, License token verification, and Webhook consistency and idempotency.
  3. Validate behavior with explicit outcomes and failure-mode tests.
  4. Produce evidence artifacts suitable for review, support, and iteration.

2. All Theory Needed (Per-Concept Breakdown)

2.1 Entitlement matrix modeling

  • Fundamentals: This concept defines the first architectural boundary for this project. You should know the invariant conditions that must remain true during normal operation and failure operation. In Stream Deck plugin work, the most useful mindset is to treat interaction paths as explicit contracts, not ad-hoc callbacks, so behavior remains deterministic under context churn and profile switching.
  • Deep Dive into the concept: For this project, Entitlement matrix modeling is where correctness begins. Model state transitions explicitly, define allowed events, and reject illegal transitions early. Tie every side effect to context identity and traceability fields so debugging can reconstruct the full sequence. Design your test plan around race-prone paths first. Add failure classes and recovery transitions before polishing UX. This creates robust behavior under load and avoids hidden coupling across action instances.
  • How this fit on projects: This concept is the primary driver of runtime correctness in this project.
  • Definitions & key terms: invariant, transition contract, failure class, recovery path.
  • Mental model diagram:
Intent -> Validate -> Reduce -> Persist -> Render
  ^                                       |
  +--------------- Recover/Retry <--------+
  • How it works: model inputs, validate boundaries, reduce deterministic state, emit minimal side effects, then observe and recover.
  • Minimal concrete example:
PSEUDOCODE
if !isValid(event, state):
  return rejectWithHint()
next = reduce(state, event)
apply(next)
  • Common misconceptions: fast prototypes do not remove the need for explicit invariants.
  • Check-your-understanding questions: Which invalid transition causes highest user impact? Why?
  • Check-your-understanding answers: Any transition that mutates irreversible state without confirmation.
  • Real-world applications: production plugins that must survive long sessions and rapid profile switches.
  • Where you will apply it: project runtime handlers and teardown logic.
  • References: Stream Deck SDK docs + main sprint Theory Primer concepts 1/2/6.
  • Key insights: deterministic state design scales better than callback patching.
  • Summary: make invalid states unrepresentable and observable.
  • Homework/Exercises to practice the concept: draw one transition table and one failure table.
  • Solutions to the homework/exercises: each transition/failure should map to explicit UI feedback and test case.

2.2 License token verification

  • Fundamentals: License token verification handles data integrity and long-lived behavior. Treat user configuration, entitlement, and environment state as a schema-governed domain.
  • Deep Dive into the concept: Build validation at every boundary: PI input, backend receive, persistence write, and migration load. Use explicit versioning and conflict policy so stale updates cannot silently win. If sensitive fields exist, isolate them through secret-safe adapters and redact all diagnostics. This prevents corruption, race bugs, and support incidents that usually appear only after release.
  • How this fit on projects: ensures reliable persistence and predictable restart/recovery behavior.
  • Definitions & key terms: schema, migration, revision, redaction.
  • Mental model diagram:
Input Delta -> Merge -> Validate -> Version -> Commit -> Observe
  • How it works: merge safely, validate strictly, commit atomically, expose clear error feedback.
  • Minimal concrete example:
PSEUDOCODE
merged = merge(prev, delta)
assert schemaValid(merged)
save(merged, revision+1)
  • Common misconceptions: compile-time types are not runtime safety.
  • Check-your-understanding questions: Why must backend revalidate PI values?
  • Check-your-understanding answers: PI can be stale/malformed; backend is source of truth.
  • Real-world applications: paid plugins, sync features, and multi-account integrations.
  • Where you will apply it: persistence, entitlement checks, and API credential handling.
  • References: Stream Deck settings/secrets docs + RFC security guidance where applicable.
  • Key insights: data integrity is a user-visible feature.
  • Summary: strict boundaries prevent expensive post-release bugs.
  • Homework/Exercises to practice the concept: define v1/v2 schema and migration tests.
  • Solutions to the homework/exercises: include defaults, backward compatibility, and rollback path.

2.3 Webhook consistency and idempotency

  • Fundamentals: Webhook consistency and idempotency translates implementation quality into user trust, adoption, and maintainability.
  • Deep Dive into the concept: Build release and support workflows in parallel with features. Define observability schema, packaging checks, and non-functional budgets (latency, memory, retry behavior). Add diagnostics UX so users can self-report actionable data. If this project targets commercial outcomes, connect operational quality to listing confidence and retention. For hardware-diverse use cases, ensure adaptive behavior is explicitly tested across capability subsets.
  • How this fit on projects: provides the delivery and sustainment layer beyond core functionality.
  • Definitions & key terms: SLA mindset, supportability, release gate, degraded mode.
  • Mental model diagram:
Feature Build -> Validation Gate -> Pack/Release -> Observe -> Support -> Improve
  • How it works: define quality gates, ship artifacts, monitor signals, feed incidents back into design.
  • Minimal concrete example:
PSEUDOCHECKLIST
validate pass
smoke install pass
diagnostics export pass
rollback artifact present
  • Common misconceptions: once it works locally, release risk is low.
  • Check-your-understanding questions: Which quality gate catches packaging regressions earliest?
  • Check-your-understanding answers: deterministic CLI validate/pack + smoke install checks.
  • Real-world applications: marketplace submission, enterprise team deployment, paid support.
  • Where you will apply it: release checklist, diagnostics, and post-launch iteration.
  • References: Stream Deck CLI docs, marketplace docs, and reliability references.
  • Key insights: sustainable plugins are operated products, not one-off scripts.
  • Summary: build supportability and release discipline into the first milestone.
  • Homework/Exercises to practice the concept: create one pre-release gate matrix and one incident response runbook.
  • Solutions to the homework/exercises: each gate/runbook step must include pass/fail evidence.

3. Project Specification

3.1 What You Will Build

A freemium plugin with feature gates, license activation, offline grace mode, and revocation handling.

3.2 Functional Requirements

  1. Implement all user-facing behaviors listed in the source sprint project.
  2. Preserve deterministic state behavior under context churn and restart.
  3. Enforce boundary validation for configuration and external events.
  4. Expose clear feedback for success, pending, and failure modes.
  5. Provide release/support artifacts aligned with project scope.

3.3 Non-Functional Requirements

  • Performance: Remain responsive under expected event rates for this project.
  • Reliability: No orphaned timers/subscriptions after teardown paths.
  • Usability: Users can understand current state from key/PI feedback quickly.
  • Supportability: Logs and diagnostics must be actionable and redacted.

3.4 Example Usage / Output

“How do I enforce paid access fairly and securely without breaking critical workflows when billing systems are temporarily unavailable?”

3.5 Real World Outcome

User can install and use core free features immediately. Premium features show clear upgrade prompts. After entering a valid license key (or signing in), premium actions unlock. If network is temporarily unavailable, plugin remains functional within grace window and shows Offline grace: 2 days left status. Revoked keys downgrade safely without crashing action workflows.

4. Solution Architecture

4.1 High-Level Design

Stream Deck Events -> Runtime Reducer -> Capability/Policy Layer -> Side Effects
        ^                                                          |
        +---------------------- Diagnostics/Observability <--------+

4.2 Key Components

  • Action Runtime Layer: Handles event routing, context scoping, and state reduction.
  • Policy Layer: Applies validation, feature gates, retries, throttles, and safety rules.
  • Feedback Layer: Produces deterministic key/dial/PI feedback from canonical state.
  • Persistence/Integration Layer: Manages settings, secrets, sync, and external API boundaries.

4.3 Design Questions (From Sprint)

  1. Fairness model
    • What is offline grace duration and why?
    • What is downgraded immediately vs deferred on revocation?
  2. Security model
    • Which checks happen server-side only?
    • How do you detect replayed or forged activation payloads?

5. Thinking Exercise (Before Building)

Write Abuse Scenarios

List five likely bypass attempts (clock rollback, copied keys, stale entitlement cache, replay attacks, webhook spoofing) and map one concrete mitigation per attempt.

6. Implementation Hints in Layers

Hint 1: Starting Point

  • Define entitlement states before implementing UI.

Hint 2: Next Level

  • Cache signed entitlement with expiry and issue time.

Hint 3: Technical Details

PSEUDOFLOW
activate -> verify server signature -> cache entitlement(expiry) -> enforce per action -> periodic revalidate

Hint 4: Tools/Debugging

  • Simulate webhook duplicates and confirm no double-upgrade/double-revoke side effects.

7. Verification and Testing Plan

  1. Unit-level: transition validity, schema validation, and policy decisions.
  2. Integration-level: PI/backend flow, persistence/restart, and dependency adapters.
  3. Failure-level: network/auth/retry/teardown behavior under injected faults.
  4. Release-level: validate/pack/smoke workflow and artifact integrity checks.

8. Interview Questions

  1. “How do you prevent permanent premium unlock via offline mode abuse?”
  2. “Why should billing webhook handlers be idempotent?”
  3. “How do you communicate downgrade reasons without exposing sensitive account details?”
  4. “Where do you store license assertions locally?”
  5. “What happens when your license API is down during startup?”

9. Common Pitfalls and Debugging

Problem 1: “Premium unlocks inconsistently across restarts”

  • Why: Entitlement cache not versioned or signature not revalidated.
  • Fix: Store versioned signed claims with explicit expiry and validation path.
  • Quick test: Restart plugin repeatedly in offline mode and verify deterministic tier state.

10. Definition of Done

  • Free tier limits are explicit and enforced.
  • License key activation validates against backend securely.
  • Offline grace mode works with bounded duration and clear UI status.
  • Revocation handling downgrades safely without data corruption.
  • Optional Stripe subscription webhook flow is idempotent.
  • Upgrade flow is clear, non-intrusive, and measurable.

11. Additional Notes

  • Why this project matters: It introduces the monetization architecture required to turn plugin usage into sustainable product revenue.
  • Source sprint project file: P20-freemium-plugin-license-activation.md
  • Traceability: Generated from ### Project 20 in the sprint guide.