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/context.md

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+# Execution context
+
+Status: target design with a partial native-development implementation.
+[ACT-1](../plans/2026-09-07_agent-context-templates-and-migration.md) governs rollout.
+
+Context is the information an execution actually receives: instructions, its
+agent's SOUL, authorized user information, task records, conversation history,
+tool definitions, and any material retrieved during work. A file's presence in
+the repository does not mean it was injected.
+
+## Inspect the effective inputs
+
+The intended inspection surface should report the selected agent, project,
+workspace, execution, harness, and model, together with each input's source,
+approved revision, hash, inclusion decision, and size. Report exclusions and
+their reasons. Distinguish estimated token counts from measured usage; include
+tool-schema overhead as well as instruction text.
+
+Exactly one agent-owned SOUL is eligible. Root and shared-default SOULs are not
+fallbacks in the target design. Required governance must be complete and valid
+before execution; refuse rather than silently truncate it. Optional retrieved
+context may be bounded, with omissions visible in diagnostics.
+
+Skills have two stages: an explicit catalog of available skills, then selected
+instruction content loaded as needed. Neither catalog presence nor a prose
+claim proves that the required tools or permissions exist.
+
+## Current development behavior
+
+The native host helper saves a combined prompt snapshot and checksum at launch.
+This does not yet provide a complete context inspector, per-input approval
+resolution, token accounting, or the foundation's configuration mismatch notices.
+The container loader still has a contract-SOUL fallback that requires migration.
+
+Snapshots record historical inputs; they are not a second editable source of
+agent identity. Current approved inputs are resolved at each Resume or Fresh
+launch. An already-running execution must not silently reload edited files.
+
+See [prompt composition](system-prompt.md), [SOUL](soul.md), and
+[behavior tests](agent-behavior-tests.md). ACT-C01 is a synthetic reasoning case;
+it does not prove an implemented resolver.