Evolution — Beyond Code

Evolving the reliable Studio 5 system into a long-lived platform.

The Situation

Studio 5 made the systems reliable: bounded retries, idempotent dispatch, safe fallbacks, and regression checks. Now the requirements are changing underneath them. Delivery priority must take a risk score into account, the knowledge engine must accept a user’s intent alongside the query, and the virtual world needs a new movement rule — all without breaking the clients and data that depend on today’s behavior. The challenge is no longer keeping the system working; it is changing it while it keeps working. The pressure points:

new business rules that must coexist with legacy behavior
API evolution without breaking existing consumers
data migrations that must be reversible
feature rollout risk in production environments

Engineering Brief

Deliver new capabilities while preserving Studio 5 trust guarantees.

Required outcomes:

introduce versioned behavior behind stable contracts
support compatibility mode for old clients
add explicit migration path and rollback trigger
preserve reliability checks from Studio 5
define evolution governance: when old behavior is deprecated, the date it is removed (its sunset), and who owns each decision

Implementation guidance:

use additive changes before breaking replacements
isolate v1 and v2 differences behind a strategy or adapter extension point
treat migration as code, not informal operations notes
gate rollout with measurable signals and exit criteria

Implementation In Nex

Suggested files:

evolution_types.nex
delivery_evolution.nex
knowledge_evolution.nex
world_evolution.nex
migration_runner.nex
studio_6_main.nex

Shared Evolution Types

class Evolution_Result
create
  make(status: String, value: String, mode: String) do
    this.status := status
    this.value := value
    this.mode := mode
  end
feature
  status: String
  value: String
  mode: String
invariant
  status_present: status /= ""
  value_present: value /= ""
  mode_present: mode /= ""
end

class Rollout_Config
create
  make(use_v2: Boolean, compatibility_mode: Boolean) do
    this.use_v2 := use_v2
    this.compatibility_mode := compatibility_mode
  end
feature
  use_v2: Boolean
  compatibility_mode: Boolean
end

Delivery Evolution (Policy V1 to V2)

Continuation from Studio 5 delivery reliability flow.

class Delivery_Policy_V1
feature
  decide_priority(tier: String): String
  require
    tier_present: tier /= ""
  do
    if tier = "PREMIUM" then
      result := "FAST_TRACK"
    else
      result := "STANDARD_TRACK"
    end
  ensure
    known_result: result = "FAST_TRACK" or result = "STANDARD_TRACK"
  end
end

class Delivery_Policy_V2
feature
  decide_priority(tier: String, risk_score: Integer): String
  require
    tier_present: tier /= ""
    risk_non_negative: risk_score >= 0
  do
    if tier = "PREMIUM" and risk_score < 50 then
      result := "FAST_TRACK"
    elseif tier = "PREMIUM" then
      result := "SAFE_TRACK"
    else
      result := "STANDARD_TRACK"
    end
  ensure
    known_result:
      result = "FAST_TRACK" or
      result = "SAFE_TRACK" or
      result = "STANDARD_TRACK"
  end
end

class Delivery_Evolution_Service
create
  make(
    v1: Delivery_Policy_V1,
    v2: Delivery_Policy_V2,
    config: Rollout_Config
  ) do
    this.v1 := v1
    this.v2 := v2
    this.config := config
  end
feature
  v1: Delivery_Policy_V1
  v2: Delivery_Policy_V2
  config: Rollout_Config

  route_mode(tier: String, risk_score: Integer): Evolution_Result
  require
    tier_present: tier /= ""
    risk_non_negative: risk_score >= 0
  do
    if config.use_v2 then
      result := create Evolution_Result.make(
        "OK",
        v2.decide_priority(tier, risk_score),
        "V2"
      )
    else
      result := create Evolution_Result.make(
        "OK",
        v1.decide_priority(tier),
        "V1"
      )
    end
  ensure
    ok_status: result.status = "OK"
  end
end

Knowledge Evolution (Compatibility Adapter)

Continuation from Studio 5 safe query and fallback logic.

class Knowledge_Query_V1
feature
  run(query: String): String
  require
    query_present: query /= ""
  do
    result := "DOC:K-LEGACY"
  ensure
    non_empty: result /= ""
  end
end

class Knowledge_Query_V2
feature
  run(query: String, intent: String): String
  require
    query_present: query /= ""
    intent_present: intent /= ""
  do
    if intent = "deep" then
      result := "DOC:K-DEEP"
    else
      result := "DOC:K-FAST"
    end
  ensure
    non_empty: result /= ""
  end
end

class Knowledge_Compatibility_Adapter
create
  make(v2: Knowledge_Query_V2) do
    this.v2 := v2
  end
feature
  v2: Knowledge_Query_V2

  run_v1_shape(query: String): String
  require
    query_present: query /= ""
  do
    result := v2.run(query, "fast")
  ensure
    non_empty: result /= ""
  end
end

class Knowledge_Evolution_Service
create
  make(
    v1: Knowledge_Query_V1,
    v1_on_v2: Knowledge_Compatibility_Adapter,
    config: Rollout_Config
  ) do
    this.v1 := v1
    this.v1_on_v2 := v1_on_v2
    this.config := config
  end
feature
  v1: Knowledge_Query_V1
  v1_on_v2: Knowledge_Compatibility_Adapter
  config: Rollout_Config

  query(query: String): Evolution_Result
  require
    query_present: query /= ""
  do
    if config.use_v2 and not config.compatibility_mode then
      result := create Evolution_Result.make(
        "OK",
        "DOC:K-DEEP",
        "V2_NATIVE"
      )
    elseif config.use_v2 then
      result := create Evolution_Result.make(
        "OK",
        v1_on_v2.run_v1_shape(query),
        "V2_COMPAT"
      )
    else
      result := create Evolution_Result.make(
        "OK",
        v1.run(query),
        "V1"
      )
    end
  ensure
    ok_status: result.status = "OK"
  end
end

World Evolution (Feature Flagged Rule Extension)

Continuation from Studio 5 safe world-step behavior.

class World_Rules_V1
feature
  apply(x: Integer, delta: Integer, max_x: Integer): Integer
  require
    max_valid: max_x >= 0
  do
    let next: Integer := x + delta
    if next < 0 then
      result := 0
    elseif next > max_x then
      result := max_x
    else
      result := next
    end
  ensure
    bounded: result >= 0 and result <= max_x
  end
end

class World_Rules_V2
feature
  apply(x: Integer, delta: Integer, max_x: Integer): Integer
  require
    max_valid: max_x >= 0
  do
    -- New damping rule for safer high-velocity transitions.
    let effective_delta: Integer := delta
    if delta > 3 then
      effective_delta := 3
    elseif delta < -3 then
      effective_delta := -3
    end

    let next: Integer := x + effective_delta
    if next < 0 then
      result := 0
    elseif next > max_x then
      result := max_x
    else
      result := next
    end
  ensure
    bounded: result >= 0 and result <= max_x
  end
end

class World_Evolution_Service
create
  make(
    v1: World_Rules_V1,
    v2: World_Rules_V2,
    config: Rollout_Config
  ) do
    this.v1 := v1
    this.v2 := v2
    this.config := config
  end
feature
  v1: World_Rules_V1
  v2: World_Rules_V2
  config: Rollout_Config

  step(x: Integer, delta: Integer, max_x: Integer): Evolution_Result
  require
    max_valid: max_x >= 0
  do
    if config.use_v2 then
      result := create Evolution_Result.make(
        "OK",
        "X=" + v2.apply(x, delta, max_x),
        "V2"
      )
    else
      result := create Evolution_Result.make(
        "OK",
        "X=" + v1.apply(x, delta, max_x),
        "V1"
      )
    end
  ensure
    ok_status: result.status = "OK"
  end
end

Migration Runner and Rollback Trigger

class Migration_Runner
create
  make(initial_count: Integer) do
    this.migrated_count := initial_count
  end
feature
  migrated_count: Integer

  run(canary_passed: Boolean): String
  do
    if canary_passed then
      migrated_count := migrated_count + 100
      result := "MIGRATION_CONTINUE"
    else
      result := "ROLLBACK"
    end
  ensure
    known_result: result = "MIGRATION_CONTINUE" or result = "ROLLBACK"
  end
end

class App
feature
  run() do
    let cfg: Rollout_Config := create Rollout_Config.make(true, true)

    -- Delivery evolution
    let d1: Delivery_Policy_V1 := create Delivery_Policy_V1
    let d2: Delivery_Policy_V2 := create Delivery_Policy_V2
    let de: Delivery_Evolution_Service
      := create Delivery_Evolution_Service.make(d1, d2, cfg)

    let dr: Evolution_Result := de.route_mode("PREMIUM", 70)
    print("Delivery: mode=" + dr.mode + " value=" + dr.value)

    -- Knowledge evolution
    let k1: Knowledge_Query_V1 := create Knowledge_Query_V1
    let kv2: Knowledge_Query_V2 := create Knowledge_Query_V2
    let ka: Knowledge_Compatibility_Adapter
      := create Knowledge_Compatibility_Adapter.make(kv2)
    let ke: Knowledge_Evolution_Service
      := create Knowledge_Evolution_Service.make(k1, ka, cfg)

    let kr: Evolution_Result := ke.query("contracts")
    print("Knowledge: mode=" + kr.mode + " value=" + kr.value)

    -- World evolution
    let w1: World_Rules_V1 := create World_Rules_V1
    let w2: World_Rules_V2 := create World_Rules_V2
    let we: World_Evolution_Service
      := create World_Evolution_Service.make(w1, w2, cfg)

    let wr: Evolution_Result := we.step(8, 6, 10)
    print("World: mode=" + wr.mode + " value=" + wr.value)

    -- Migration + rollback gate
    let m: Migration_Runner := create Migration_Runner.make(0)
    print("Migration gate: " + m.run(true))
    print("Migration count: " + m.migrated_count)
    print("Rollback gate: " + m.run(false))
  end
end

Expected outcomes:

v2 behavior can be rolled out without breaking v1 clients
compatibility mode supports gradual client migration
migration continues only when canary checks pass (checks run on a small share of traffic before full rollout)
rollback condition is explicit and executable

Studio Challenges

Level 1 — One Evolution Path

evolve one Studio 5 service from v1 to v2 behind a stable contract
add compatibility mode
prove old client behavior still works

Level 2 — Coordinated Multi-Domain Evolution

add v2 behavior for delivery, knowledge, and world
define one shared rollout policy
show canary and rollback behavior with run logs

Level 3 — Future-Proofing Drill

simulate two additional future changes
evaluate whether current extension points absorb them cleanly
define deprecation timeline and ownership

Postmortem

Discuss with evidence:

Which extension point was most valuable for safe evolution?
Which compatibility costs were worth paying?
What should be deprecated next, and when?
Which metrics should gate future rollouts?

Deliverables

versioning plan (a map of v1 and v2 behavior)
compatibility matrix (client version against service mode)
migration and rollback playbook with gate conditions
updated Nex code and evolution run logs
deprecation roadmap with dates and owners

Exit Criteria

We are ready for Part IX if:

critical services evolve through versioned extension points, not rewrites
compatibility behavior is explicit and tested
migration and rollback are operationally defined
reliability guarantees from Studio 5 remain intact during evolution