Use shared assets instead of prompt prefix change detectors

docs/roadmap/implementation.md

@@ -33,17 +33,17 @@ The following decisions are complete and are not implementation-time choices:
   registration, or erase typed artifact relationships outside existing
   framework boundaries.
 - Exact cache identity means equal ordered message roles, content bytes, and
-  cache-control values after Scriptorium has rendered the prompt. Tests must
-  use `scriptorium.PreparedRun.Messages`; comparing source Markdown is
-  insufficient.
+  cache-control values after Scriptorium has rendered the prompt. Enforce this
+  primarily through one canonical shared asset per shared message and document
+  the expected order and cache-control policy.
 - Scriptorium and provider-specific types remain confined to the LLM runtime,
   prompt-asset wiring, and their tests. Production extractors continue to use
   only Notarius contracts.
 - Default tests remain offline, deterministic, and credential-free. Live model
   evaluation is an explicit manual acceptance activity, not part of
   `go test ./...`.
-- Avoid broad snapshots. Exact byte assertions are warranted only for the
-  rendered common message prefixes because byte identity is the feature.
+- Do not add message-count, common-prefix-length, or complete rendered-prompt
+  snapshots. They are change detectors rather than durable behavioral tests.
 - Update current-behavior documentation only in the stage that changes that
   behavior. Do not describe a partially implemented later stage as complete.
 
@@ -100,34 +100,21 @@ spell/combat breakpoint. Use no more than these four markers so the request
 remains portable across the configured backends; do not add module-specific
 markers in this work.
 
-## Stage 1: Characterize The Rendered Cache Boundary
+## Stage 1: Protect Shared Input Behavior And Baseline Prompt Wiring
 
 ### Goal
 
-Protect the current three-message common prefix and establish reusable test
-support before changing prompt composition.
+Protect deterministic shared input rendering and confirm the existing prompt
+assets prepare successfully before changing prompt composition.
 
 ### Implementation
 
-1. Add a cross-lane prompt test under
-   `internal/modules/dnd/shared`, using the external test package
-   `shared_test` so it can import all three extractor packages without an
-   import cycle.
-2. In one `llm.AssetRegistry`, register spell, NPC, and combat prompt assets.
-   Build one offline Scriptorium engine with one test profile and use
-   `Engine.Prepare` for every prompt. Supply identical transcript, players,
-   party, and glossary inputs. Supply the same unbound NPC JSON to spell and
-   combat, plus the spell catalog required only by spells.
-3. Add a small test helper that compares an expected prefix of
-   `[]scriptorium.RenderedMessage` field by field: role, exact content string,
-   and a canonical JSON representation of cache control. Do not compare prompt
-   IDs, rendered prompt hashes, output contracts, or schemas across modules;
-   those are intentionally different.
-4. Assert that the first three messages are identical across all lanes and that
-   spell/combat NPC grounding is identical at their current corresponding
-   position. Assert the existing message counts separately so Stage 3 must
-   update them deliberately.
-5. Extend `internal/modules/dnd/shared/prompt_inputs_test.go` with one
+1. Retain one offline prompt preparation test in each extractor package. Each
+   test should prove registration succeeds, the prompt selects its package-owned
+   response schema, required dynamic inputs render, and no provider call or
+   credentials are required. Do not assert total message count, shared-prefix
+   length, or the complete rendered prompt.
+2. Extend `internal/modules/dnd/shared/prompt_inputs_test.go` with one
    table-driven identity test covering:
    - identical source material and references produce deeply equal common input
      materials;
@@ -135,11 +122,9 @@ support before changing prompt composition.
    - `roster` fallback produces the canonical `party` material;
    - an explicit non-empty `party` wins over `roster`; and
    - missing optional slots render the existing single-space placeholder.
-6. Do not add a second full HTTP/provider test. The Scriptorium engine's
-   prepared messages are the stable boundary owned by this repository;
-   Scriptorium owns provider request serialization. Existing LLM adapter tests
-   continue to prove that prepared message order and content reach the engine
-   request.
+3. Do not add a full HTTP/provider test for cross-module prompt equality.
+   Scriptorium owns provider request serialization, and shared asset ownership
+   removes the duplicated content that would otherwise need equality testing.
 
 ### Verification
 
@@ -151,10 +136,10 @@ go test ./internal/modules/dnd/shared ./internal/modules/dnd/extract/spells ./in
 
 ### Completion Criteria
 
-- The new cross-lane test fails if any role, content byte, cache-control value,
-  or order within the intended common prefix differs.
-- Tests distinguish intended prompt identity from intentionally different
-  prompt IDs, schemas, and module-specific suffixes.
+- Shared input tests protect deterministic serialization and canonical slot
+  handling.
+- Each extractor's existing behavior-level asset test prepares successfully
+  without pinning message count or prefix boundaries.
 - No production behavior changes in this stage.
 
 ## Stage 2: Make Prompt Asset Manifests Exact
@@ -233,8 +218,8 @@ go test ./internal/framework/promptfs ./internal/modules/dnd/shared ./internal/m
 
 ### Goal
 
-Implement the exact target prompt layout defined above and maximize the
-byte-identical all-lane and spell/combat prefixes.
+Implement the target prompt layout defined above using canonical shared assets
+and maximize the reusable all-lane and spell/combat content.
 
 ### Implementation
 
@@ -257,17 +242,12 @@ byte-identical all-lane and spell/combat prefixes.
    `Return exactly one JSON object` rule through the common evidence message.
 6. Keep the spell catalog input and NPC registry input byte generation
    unchanged. Keep the NPC extractor free of an `npcs` input.
-7. Update package asset tests for new message counts and positions. Replace
-   content-substring assertions for moved common policy with assertions in the
-   cross-lane rendered-prefix test.
-8. Update the cross-lane test to assert:
-   - indices 0 through 4 are identical for all three lanes when common inputs
-     are identical;
-   - indices 0 through 2 remain identical when transcript and references differ;
-   - spell and combat indices 5 and 6 are identical for the same NPC registry;
-   - the shared prefixes end at the exact indices in the table; and
-   - module-specific suffixes are not accidentally identical or reordered.
-9. Update `docs/internal/modules.md` and `docs/internal/llm.md` in the same
+7. Update package asset tests only for behavioral wiring: prompt preparation,
+   response schema selection, and required dynamic input rendering. Do not add
+   assertions for total message count, exact shared-prefix length, or the end
+   index of a shared section. The shared manifest tests own canonical asset
+   selection.
+8. Update `docs/internal/modules.md` and `docs/internal/llm.md` in the same
    change to describe the implemented common-prefix composition, exact prompt
    manifest fingerprinting, and cache-control placement. Describe current
    behavior, not this staged plan.
@@ -283,8 +263,9 @@ go test ./internal/framework/llm
 
 ### Completion Criteria
 
-- Prepared messages match the target table exactly.
 - Shared rules exist in one embedded file and have no local paraphrased copy.
+- Every applicable prompt references those shared assets in the documented
+  order and with the documented cache-control policy.
 - Prompt fingerprints change for the intentional prompt contract change and
   include every newly rendered asset.
 - No artifact schema, durable representation, module selection, or reference
@@ -339,7 +320,7 @@ go test ./internal/modules/dnd/shared ./internal/modules/dnd/extract/spells ./in
 
 - Only one production implementation prepares chunk prompt material.
 - Extractor behavior and public errors retain useful module context.
-- The rendered prompt identity tests still pass.
+- Prompt preparation and shared input behavior tests still pass.
 
 ## Stage 5: Share Cited Source Traversal
 
@@ -534,7 +515,7 @@ default test suite.
    the fixed decision for this plan is to leave them package-owned and separate.
 4. Consolidate redundant tests created by intermediate stages. Retain:
    - one shared manifest test suite;
-   - one exact rendered-prefix suite;
+   - behavior-level prompt preparation tests without prefix-length snapshots;
    - focused package tests for artifact-specific prompts and validators; and
    - existing production registration contract coverage.
 5. Update `docs/internal/modules.md` and `docs/internal/llm.md` so they are the