docs: concept annexation, provider/reference docs, ACT-1 groundwork

Mosaic concepts pages now own the adapted content; source/license
metadata under docs/reference/concepts. Adds ACT-1 agent-context
planning capture, pinned concept test package + preparation utility,
foundation observation notes (durability, evidence, federation,
onboarding, workflow), and the #1495 consolidation assessment.
TOOLS.md updated for the host-dev launcher.

docs/concepts/system-prompt.md

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+# Prompt composition
+
+Status: target responsibilities agreed; unified resolution remains planned.
+The existing demo's launch and verification contracts remain in force.
+
+Mosaic composes instructions from sources with distinct ownership and lifetimes.
+The composition contract must be explicit and testable across supported harnesses.
+
+| Source | Responsibility |
+|---|---|
+| CONSTITUTION | Shared boundaries, principles and authority |
+| STANDARDS | Quality expectations and evidence requirements |
+| Agent SOUL | Voice, temperament and interaction style |
+| Repository AGENTS | Applicable repository procedures |
+| Scoped USER context | Relevant, authorized user preferences |
+| Runtime context | Actual identity, workspace, tools, skills and session behavior |
+| Assignment records | Authorized work, current state and acceptance criteria |
+
+## Resolution rules
+
+Select one canonical SOUL belonging to the requested agent. A project folder,
+template, root SOUL, or shared boilerplate must not replace it implicitly.
+System bootstrap creates the initial agent's instance from a reviewed template;
+later agent bootstrap follows the same ownership rule. Templates are not runtime
+personality layers. Updating them must not silently overwrite existing instances.
+
+Load repository procedures only where applicable to the execution's scope.
+Do not automatically give a worker the conductor's context or privileges.
+User preferences, agent style, and retrieved content cannot widen permission.
+Heading order in a concatenated Markdown file is not security enforcement.
+
+## Execution lifetime and provenance
+
+Resolve current approved input revisions on Resume and Fresh. Record their
+identity with the execution, and preserve the exact injected snapshot where
+required. Keep credentials out of ordinary prompt records. Permission enforcement
+belongs to the runtime and policy mechanisms, not the personality file.
+
+A harness may contribute its own instructions. Distinguish Mosaic's assembled
+inputs from a verified model-bound request; a local prompt snapshot alone cannot
+establish what an external harness added.
+
+## Current implementation boundary
+
+The container replaces Pi's base prompt with generated context; native development
+appends context to Pi's coding prompt. They differ in source selection and policy
+enforcement. Reconcile those paths under ACT-1 after demo validation. Do not remove
+POC startup-marker behavior before replacement verification fixtures are tested.
+
+See [context inspection](context.md), [runtime ownership](agent-runtimes.md), and
+[the migration plan](../plans/2026-09-07_agent-context-templates-and-migration.md).