refactor(acp): split oversized service into focused modules

[yan-ad]

Summary

Split src/acp/service.rs into a private service/ module tree without changing behavior. The original file is 5,549 lines at the updated #64 head; service/mod.rs is now 190 lines and every extracted file is now at most 374 lines, including adjacent test files.

Depends on #64. This branch starts from #64's current head, including the compaction-mode tooltip follow-up. Please merge #64 first; until then GitHub's diff against main also includes that prerequisite. The refactor commits are above #64; the latest follow-up further narrows module responsibilities.

Closes #65.

Module boundaries

• mod.rs: service/session state, capabilities, shared cancellation and error helpers.
• sessions.rs: new/load/resume/fork/list/close/delete/cancel and persisted attachment handling.
• prompt.rs and stream.rs: prompt preparation, execution, stream events, transcript recording, and turn finalization.
• compaction.rs: explicit/automatic compaction, summary generation, transcript replacement, and notifications.
• usage.rs: provider context measurements, live usage, cumulative billing, and ACP usage updates.
• config.rs: MCP config, modes, model/reasoning selection, limits, and picker descriptions.
• commands.rs: command advertisement, expansion, and side questions.
• attachments.rs: input conversion, image/audio storage, and rollback guard.
• permissions.rs, questions.rs, and terminals.rs: permission previews/grants, elicitation, and client-terminal bridging/cleanup.
• notifications.rs: text/tool projections, locations/diffs/media, and transcript replay.
• test_support.rs: shared test fixtures, compiled only under cfg(test).

Tests move alongside their owners; stdio integration tests stay in tests/acp_stdio.rs. Production imports are explicit, child modules remain private, sibling-used helpers use pub(super), and the server-facing service::AcpService API is unchanged.

Behavior preservation

No changes to function bodies, public signatures, lock scopes, persistence ordering, cancellation handling, compaction thresholds, context-versus-billing semantics, or terminal cleanup. Compared all 202 functions/methods/types/fixtures/tests against #64 using Rust syntax parsing: production function and method bodies are token-identical; moved test bodies differ only in formatting-only trailing commas. Only internal type/field visibility and import/module placement change.

Validation

• cargo test acp:: --bin crabcode: 76 passed.
• cargo test session::compaction:: --bin crabcode: 21 passed.
• cargo test --test acp_stdio: 8 passed, including automatic compaction and serialized mode descriptions.
• cargo fmt --all -- --check and git diff --check: passed.
• Serial full-unit run before the tooltip follow-up: 1,850 passed, 3 ignored, one existing unrelated failure in ui::components::chat::tests::test_edit_tool_renders_codex_style_diff_summary. It embeds /Users/carlo/Desktop/Projects/crabcode and expects a basename on other checkouts; the same failure is documented in fix(acp): trigger automatic compaction from provider context usage #64.

Synced to yan-ad/crabcode:yan-flavor (refactor commit ac52d96, latest smaller-module sync head ca801fe), preserving that branch's older lifecycle implementation and concurrent install/upgrade changes. Flavor validation: 61 ACP tests, 21 compaction tests, and 4 stdio tests pass. Five consecutive parallel stdio runs pass after test-only fixtures eliminated models.dev and Ollama discovery dependencies. All 181 flavor functions/types/fixtures/tests are preserved, with function and test bodies token-identical to the flavor baseline.

Follow-up: smaller source chunks

The smaller-module follow-up (3189129) separates models, modes, and MCP config; tool content, tool locations, and replay; attachment storage; command expansion; permission previews; context accounting; transcript recording; and compaction summary construction. Long lifecycle tests are in adjacent service/tests/ files, still compiled as child modules of their owners.

This is source organization, not Rust minification or a change to model context size. Related execution flows remain intact rather than splitting functions to satisfy an arbitrary line count. Upstream's largest file is now 374 lines (previously 622); the shared core remains 202 lines. The adapted flavor retains its existing 521-line prompt flow, with all other files at most 349 lines.

Validation after this follow-up: upstream 76 ACP tests, 21 compaction tests, and 8 stdio tests; flavor 61 ACP tests, 21 compaction tests, and 4 stdio tests. Both stdio suites pass in three consecutive complete runs. Formatting and whitespace checks pass. A separate upstream test-only follow-up (bbea752) isolates mock compaction from runtime-provider discovery without altering authentication tests.