Implement verified source adapters and context normalization

[andrewperis]

Parent epic: #5

Summary

Implement verified source adapters and context normalization for Context Builder v1.

Ownership and dependencies

• Repositories: platform.
• Depends on: Define versioned Context Builder request, source and result contracts #76, Implement Context Builder authorization and source-access policy #77.
• Baseline: Prompt SDK v1.0.0 and Context Package v1.0.0.

Scope and deliverables

• Add provider-neutral readers for explicit caller-supplied/synthetic artifacts, pinned public canon snapshots and approved private-export bytes from an injected authorized reader.
• Verify full immutable reference tuples and byte identity before parsing; disallow live branch resolution, repository cloning and implicit network fetches.
• Normalize supported UTF-8 text/JSON into candidates with stable IDs, exact versions, classification, source/fragment evidence, validity and canon/continuity metadata.
• Define invalid encoding, duplicate JSON keys, unsupported formats, conflicting source versions, resource bounds and deterministic chunk/fragment identity.

Acceptance criteria

• Identical approved source bytes produce identical normalized candidates and lineage.
• Corrupted bytes, missing references, traversal/symlink escapes and oversized inputs fail safely.
• Private support uses synthetic fixtures and an injected approved-export reader; no real Lore content or credentials are required.
• Source-provided instructions are treated as data and cannot change access policy, selection policy or authority.

Implementation guardrails

Follow Constitution v1.0.0 at a9cc8a503aa30e17820edc62ac95f7cbe10e0564 and repository boundaries. Add focused tests with implementation; the later suite task consolidates rather than postpones testing. Public issues, fixtures and docs use synthetic/already-public material only. Approved private inputs stay behind explicit secure artifact boundaries. No direct Lore checkout, silent declassification, self-approval or canon promotion.