Unify the split Effect DI graphs (AppLayer vs. LayerNode) #10

Why

The server has two independent, hand-maintained dependency-injection graphs for
Effect services, and nothing keeps them in sync. A service can be fully and
correctly wired into one and silently absent from the other — TypeScript
typechecks each graph independently and cannot see the gap.

Graph A — legacy, hand-rolled, no compile-time dependency check.
packages/opencode/src/effect/app-runtime.ts builds AppLayer via
Layer.mergeAll(...) over ~40 X.defaultLayer exports, where each
defaultLayer is manually written as
layer.pipe(Layer.provide(Dep1.defaultLayer), Layer.provide(Dep2.defaultLayer), ...).
packages/opencode/src/effect/bootstrap-runtime.ts (BootstrapLayer) and
packages/opencode/src/session/prompt.ts (SessionPrompt.defaultLayer) follow
the same style. Nothing checks that a .pipe(Layer.provide(...)) chain
actually lists every dependency the wrapped layer needs — a missing entry is a
silent gap, not a compile error.

Graph B — LayerNode, compile-time-checked.
packages/core/src/effect/layer-node.ts defines LayerNode.make(layer, deps)
and LayerNode.group(nodes). Its CheckDependencies type produces an actual
TypeScript error ({"Missing dependencies": ...}) when a node's declared
deps don't cover what the wrapped layer requires. This is the graph that
matters at runtime: packages/opencode/src/server/routes/instance/httpapi/server.ts
builds the real HTTP API server — the one every TUI session and opencode run
invocation actually talks to — from LayerNode.group([...]) /
LayerNode.buildLayer(app), not from AppLayer.

Because the two graphs are separately maintained, a service correctly added to
Graph A gives zero signal about Graph B, and vice versa. This has caused three
independent incidents:

1. 2026-08-02 (today). AutoMode.Service
   (packages/opencode/src/auto-mode/service.ts) was wired into AppLayer
   and, after a first fix attempt, into SessionPrompt.defaultLayer — but was
   never added to the LayerNode.group([...]) node list in
   server/routes/instance/httpapi/server.ts. Since that list is what
   actually serves TUI/opencode run sessions, every prompt crashed at
   runtime with Service not found: @opencode/AutoMode, even though
   bun run typecheck passed cleanly on both attempts. Fixed by adding
   AutoMode.node to server.ts's node list.
   • Side finding: SessionPrompt.defaultLayer's .pipe(Layer.provide(...))
     chain was sitting at exactly 20 arguments — TypeScript's pipe()
     overload ceiling. A 21st argument produces a hard arity error
     (TS2554: Expected 0-20 arguments, but got 21) and the whole chain's
     inferred R degrades to unknown, breaking a dozen unrelated files that
     structurally depend on that type. The workaround (folding the new layer
     into an existing Layer.mergeAll(...) argument instead of adding a new
     .pipe() slot) works but is a trap for the next person who doesn't know
     the ceiling exists.
2. 2026-07-19 (openspec/changes/intake-20260718-203617-8301aa/.skein/agent-notes.md):
   identical failure mode for PatternDetection —
   "PatternDetection.node missing from LayerNode.make at prompt.ts:1779" →
   "typecheck error + service-not-found in tests."
3. openspec/changes/retire-auto-reply/ (open, unstarted): documents the
   inverse failure mode. auto-reply, automation/automation-features,
   pattern-detection, and scheduler all export layer/defaultLayer but
   were never given a LayerNode node and never added to server.ts at
   all — so instead of crashing, they are silently inert. opencode auto-reply --enable reports success and does nothing, which that proposal calls out
   as "worse than not having it. It cost real debugging time to establish
   that it is inert."

Same root cause, three incidents, two opposite symptoms (silent no-op vs.
runtime crash) depending on which side of the split a service lands on. This
is a systemic gap, not a one-off mistake, and it will keep recurring for every
new service until the graphs are unified or guarded.

What Changes

• Audit every service that exports a legacy layer/defaultLayer pair and
  determine whether it also exports and registers a LayerNode .node in
  server/routes/instance/httpapi/server.ts's node list. Produce a complete
  mismatch list in both directions.
• Decide and document the canonical mechanism going forward. LayerNode has
  compile-time dependency checking; the legacy .pipe(Layer.provide(...))
  style does not and has a silent arity ceiling. Recommendation: migrate
  app-runtime.ts's AppLayer and bootstrap-runtime.ts's BootstrapLayer
  onto LayerNode, retiring the hand-rolled defaultLayer composition
  pattern where it duplicates what a .node already expresses.
• If a full migration is judged too large for one change, land a regression
  guard instead (e.g. a script/CI check that fails when a service has a
  defaultLayer export but no corresponding .node registered in
  server.ts, or vice versa) so this class of bug is caught before merge
  rather than at runtime.
• Flag session/prompt.ts's SessionPrompt.defaultLayer specifically — it is
  at the .pipe() argument ceiling today and the next added dependency will
  hit the same trap unless the chain is restructured (e.g. via LayerNode,
  or by pre-emptively grouping more entries into Layer.mergeAll(...)).
• Cross-reference openspec/changes/retire-auto-reply/ — its Phase 1 audit
  (auto-reply, automation-features, pattern-detection, scheduler) is the same
  "who's actually registered in the graph" question from the opposite
  direction, and should reuse this change's audit method rather than
  duplicating it.

Non-Goals

• Not rewriting every service's DI wiring in one change — this is audit,
  canonicalization decision, and (if in scope) a regression guard, not a
  wholesale rewrite.
• Not deleting the auto-reply/automation/pattern-detection/scheduler code —
  that is retire-auto-reply's job; this change only supplies the audit
  method and flags the shared root cause.

Impact

• Affected: packages/opencode/src/effect/app-runtime.ts,
  packages/opencode/src/effect/bootstrap-runtime.ts,
  packages/opencode/src/session/prompt.ts,
  packages/opencode/src/server/routes/instance/httpapi/server.ts,
  packages/core/src/effect/layer-node.ts, and every service module that
  exports defaultLayer/node.
• No user-facing behavior change is intended beyond eliminating a class of
  runtime crash / silent-dead-service bug.

Disposition (2026-09-18)

Archived — superseded/obsolete. Unified upstream (451876b): one LayerNode graph in app-runtime.ts and server.ts already includes the fork nodes. The fork's dead re-created defaultLayer graph was deleted 2026-09-18 under retire-legacy-compat-shims.