docs(agent-context): ship the "loaded metadata is read-only" anti-pattern to adopter projects

Add a Principles bullet to the always-on agent context (scaffolded into every
adopter project by `meta init` / `*:agent-docs` across all five ports): never inject
nodes or mutate the loaded metadata tree at load time — author the field in the
metadata, or derive it during codegen (read metadata → emit output). This is the
adopter-facing form of the durable rule from the AI-trace design reversal.

Regenerated the agent-context-conformance goldens (AGENTS.md + CLAUDE.md × 4 stacks)
via the shared assembler. Verified: TS agent-context conformance + size-gate 5/5;
Python agent-context conformance 5/5 (cross-port byte-identity holds with the new line).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: dmealing

agent-context/templates/always-on.md.mustache

@@ -9,6 +9,7 @@ spine; generated code is the disposable artifact. Regenerate with `{{codegenComm
 - Pattern-derivable from metadata = codegen, never hand-write (FKs, CRUD, validators, finders).
 - Never hand-edit generated files — change the metadata and regenerate (three-way merge preserves hand-written regions).
 - Use the generated constants for any string that names metadata.
+- The loaded metadata model is READ-ONLY — never inject nodes or mutate the tree at load time (no "enrich the model on load" hooks). Need an extra field/column? Author it in the metadata, or derive it during codegen (read the metadata, emit output). Mutating the loaded model makes it diverge from what's declared — a bad practice reserved for very rare cases.
 
 ## Authoring rules you must not violate
 - Nodes are fused-key maps: `{"<type>.<subType>": { ... }}` (e.g. `{"field.string": {"name": "email"}}`) — never split the type and subtype into separate keys.

fixtures/agent-context-conformance/java-kotlin-react-tanstack/expected/.metaobjects/AGENTS.md

@@ -9,6 +9,7 @@ spine; generated code is the disposable artifact. Regenerate with `mvn metaobjec
 - Pattern-derivable from metadata = codegen, never hand-write (FKs, CRUD, validators, finders).
 - Never hand-edit generated files — change the metadata and regenerate (three-way merge preserves hand-written regions).
 - Use the generated constants for any string that names metadata.
+- The loaded metadata model is READ-ONLY — never inject nodes or mutate the tree at load time (no "enrich the model on load" hooks). Need an extra field/column? Author it in the metadata, or derive it during codegen (read the metadata, emit output). Mutating the loaded model makes it diverge from what's declared — a bad practice reserved for very rare cases.
 
 ## Authoring rules you must not violate
 - Nodes are fused-key maps: `{"<type>.<subType>": { ... }}` (e.g. `{"field.string": {"name": "email"}}`) — never split the type and subtype into separate keys.

fixtures/agent-context-conformance/java-kotlin-react-tanstack/expected/.metaobjects/CLAUDE.md

@@ -9,6 +9,7 @@ spine; generated code is the disposable artifact. Regenerate with `mvn metaobjec
 - Pattern-derivable from metadata = codegen, never hand-write (FKs, CRUD, validators, finders).
 - Never hand-edit generated files — change the metadata and regenerate (three-way merge preserves hand-written regions).
 - Use the generated constants for any string that names metadata.
+- The loaded metadata model is READ-ONLY — never inject nodes or mutate the tree at load time (no "enrich the model on load" hooks). Need an extra field/column? Author it in the metadata, or derive it during codegen (read the metadata, emit output). Mutating the loaded model makes it diverge from what's declared — a bad practice reserved for very rare cases.
 
 ## Authoring rules you must not violate
 - Nodes are fused-key maps: `{"<type>.<subType>": { ... }}` (e.g. `{"field.string": {"name": "email"}}`) — never split the type and subtype into separate keys.

fixtures/agent-context-conformance/java-react/expected/.metaobjects/AGENTS.md

@@ -9,6 +9,7 @@ spine; generated code is the disposable artifact. Regenerate with `mvn metaobjec
 - Pattern-derivable from metadata = codegen, never hand-write (FKs, CRUD, validators, finders).
 - Never hand-edit generated files — change the metadata and regenerate (three-way merge preserves hand-written regions).
 - Use the generated constants for any string that names metadata.
+- The loaded metadata model is READ-ONLY — never inject nodes or mutate the tree at load time (no "enrich the model on load" hooks). Need an extra field/column? Author it in the metadata, or derive it during codegen (read the metadata, emit output). Mutating the loaded model makes it diverge from what's declared — a bad practice reserved for very rare cases.
 
 ## Authoring rules you must not violate
 - Nodes are fused-key maps: `{"<type>.<subType>": { ... }}` (e.g. `{"field.string": {"name": "email"}}`) — never split the type and subtype into separate keys.

fixtures/agent-context-conformance/java-react/expected/.metaobjects/CLAUDE.md

@@ -9,6 +9,7 @@ spine; generated code is the disposable artifact. Regenerate with `mvn metaobjec
 - Pattern-derivable from metadata = codegen, never hand-write (FKs, CRUD, validators, finders).
 - Never hand-edit generated files — change the metadata and regenerate (three-way merge preserves hand-written regions).
 - Use the generated constants for any string that names metadata.
+- The loaded metadata model is READ-ONLY — never inject nodes or mutate the tree at load time (no "enrich the model on load" hooks). Need an extra field/column? Author it in the metadata, or derive it during codegen (read the metadata, emit output). Mutating the loaded model makes it diverge from what's declared — a bad practice reserved for very rare cases.
 
 ## Authoring rules you must not violate
 - Nodes are fused-key maps: `{"<type>.<subType>": { ... }}` (e.g. `{"field.string": {"name": "email"}}`) — never split the type and subtype into separate keys.

fixtures/agent-context-conformance/python/expected/.metaobjects/AGENTS.md

@@ -9,6 +9,7 @@ spine; generated code is the disposable artifact. Regenerate with `metaobjects g
 - Pattern-derivable from metadata = codegen, never hand-write (FKs, CRUD, validators, finders).
 - Never hand-edit generated files — change the metadata and regenerate (three-way merge preserves hand-written regions).
 - Use the generated constants for any string that names metadata.
+- The loaded metadata model is READ-ONLY — never inject nodes or mutate the tree at load time (no "enrich the model on load" hooks). Need an extra field/column? Author it in the metadata, or derive it during codegen (read the metadata, emit output). Mutating the loaded model makes it diverge from what's declared — a bad practice reserved for very rare cases.
 
 ## Authoring rules you must not violate
 - Nodes are fused-key maps: `{"<type>.<subType>": { ... }}` (e.g. `{"field.string": {"name": "email"}}`) — never split the type and subtype into separate keys.

fixtures/agent-context-conformance/python/expected/.metaobjects/CLAUDE.md

@@ -9,6 +9,7 @@ spine; generated code is the disposable artifact. Regenerate with `metaobjects g
 - Pattern-derivable from metadata = codegen, never hand-write (FKs, CRUD, validators, finders).
 - Never hand-edit generated files — change the metadata and regenerate (three-way merge preserves hand-written regions).
 - Use the generated constants for any string that names metadata.
+- The loaded metadata model is READ-ONLY — never inject nodes or mutate the tree at load time (no "enrich the model on load" hooks). Need an extra field/column? Author it in the metadata, or derive it during codegen (read the metadata, emit output). Mutating the loaded model makes it diverge from what's declared — a bad practice reserved for very rare cases.
 
 ## Authoring rules you must not violate
 - Nodes are fused-key maps: `{"<type>.<subType>": { ... }}` (e.g. `{"field.string": {"name": "email"}}`) — never split the type and subtype into separate keys.

fixtures/agent-context-conformance/ts-react-tanstack/expected/.metaobjects/AGENTS.md

@@ -9,6 +9,7 @@ spine; generated code is the disposable artifact. Regenerate with `npx meta gen`
 - Pattern-derivable from metadata = codegen, never hand-write (FKs, CRUD, validators, finders).
 - Never hand-edit generated files — change the metadata and regenerate (three-way merge preserves hand-written regions).
 - Use the generated constants for any string that names metadata.
+- The loaded metadata model is READ-ONLY — never inject nodes or mutate the tree at load time (no "enrich the model on load" hooks). Need an extra field/column? Author it in the metadata, or derive it during codegen (read the metadata, emit output). Mutating the loaded model makes it diverge from what's declared — a bad practice reserved for very rare cases.
 
 ## Authoring rules you must not violate
 - Nodes are fused-key maps: `{"<type>.<subType>": { ... }}` (e.g. `{"field.string": {"name": "email"}}`) — never split the type and subtype into separate keys.

fixtures/agent-context-conformance/ts-react-tanstack/expected/.metaobjects/CLAUDE.md

@@ -9,6 +9,7 @@ spine; generated code is the disposable artifact. Regenerate with `npx meta gen`
 - Pattern-derivable from metadata = codegen, never hand-write (FKs, CRUD, validators, finders).
 - Never hand-edit generated files — change the metadata and regenerate (three-way merge preserves hand-written regions).
 - Use the generated constants for any string that names metadata.
+- The loaded metadata model is READ-ONLY — never inject nodes or mutate the tree at load time (no "enrich the model on load" hooks). Need an extra field/column? Author it in the metadata, or derive it during codegen (read the metadata, emit output). Mutating the loaded model makes it diverge from what's declared — a bad practice reserved for very rare cases.
 
 ## Authoring rules you must not violate
 - Nodes are fused-key maps: `{"<type>.<subType>": { ... }}` (e.g. `{"field.string": {"name": "email"}}`) — never split the type and subtype into separate keys.