[timesler]

Summary

Pass configured backend tool display titles to clients without adding them to model-facing content.

• Preserve backend title/annotations through Rust discovery and binding DTOs.
• Add _meta["atlassian.com/mcp-compressor/tool"] on both get_tool_schema and invoke_tool results, containing Tool-shaped metadata (name, resolved title, inputSchema, optional description/annotations).
• Attach invocation metadata after shrinking, keeping it out of text previews and truncation artifacts. Preserve unrelated response metadata.
• Display precedence: nonblank title → annotations.title → canonical name.
• No title additions to content, structuredContent, compressed listings, or Python/TypeScript schema text. Callable identity and schemas unchanged.

_meta is the standard MCP envelope; the namespaced key is a compressor-specific extension. Hosts must consume this for UI only, not serialize protocol metadata into model history. Alta's companion implementation strips it before after-hooks/history and forwards validated titles as ACP tool_call_update events. Passthrough descriptors retain upstream metadata; no protocol can prevent an arbitrary host from serializing metadata it should not expose.

This supersedes the original text/structuredContent approach; PR was closed briefly and reopened at the requester's direction.

Validation

• Rust: 341 core tests + 20 full compressed-server tests + 4 compression-level tests passed.
• Real MCP wire tests at all four compression levels verify metadata on schema/invoke responses and absence of title sentinels in model-facing fields/listings. Existing complete-result preservation test verifies unrelated metadata remains intact.
• TypeScript native rebuild + check: 127 passed with lint/format/typechecks.
• Python native rebuild + core tests: 26 passed.
• make check, docs-test, pre-commit hooks passed.

[timesler]

Closing as requested: MCP tool display titles belong to tools/list descriptors. The compressed surface advertises wrapper tools, not upstream tools, so adding a separate schema-response title contract is not appropriate. This PR is withdrawn; no release is intended.

[timesler]

Alta companion consumer: https://bitbucket.org/atlassian/alta/pull-requests/5314 — strips namespaced response metadata before after-hooks/model history and forwards validated UI titles over ACP, including durable approval resumes. No model-visible title additions.

[timesler]

Fixed SDK v2 protocol CI in b9cbeb0. Reproduced all four failures: exact envelope expectations omitted the newly added client-only metadata. Updated the full expected envelope (without relaxing checks), added distinct UI-only title sentinels and assertions for schema/invoke content isolation under modern/legacy protocol modes and TOON on/off. Exact CI command now passes all 27 tests locally; make check, docs-test and commit hooks also pass. Replacement CI is running.