fix(adapter): dedupe local-only command result output

[ran411285752]

Summary

• Deduplicate local-only slash command output at the SDK-to-ACP adapter boundary.
• Cover both the current SDK sequence (assistant then terminal result) and the local_command_output compatibility path.
• Keep evidence scoped to the originating turn or SDK cycle so ordinary assistant text and later turns are not globally deduplicated.

Root cause

A live Claude OAuth / Agent SDK 0.3.220 trace showed that /context currently emits:

assistant text: 2268 bytes
result text:    2270 bytes

The payloads are identical after removing the result's two trailing line feeds. The adapter forwarded the consolidated assistant text and then unconditionally forwarded the terminal result because the turn was classified as a local-only command.

The issue report described the first source as system/local_command_output; this PR retains coverage for that SDK shape, while also fixing the current observed assistant -> result sequence.

Implementation

• Canonicalize only newline representation and trailing line feeds for local-command comparisons.
• Retain source-identified local_command_output evidence on its Turn.
• Retain consolidated assistant evidence only for the next SDK result cycle.
• Clear cycle evidence on terminal results and non-owed idle boundaries, including autonomous, cancelled, and no-result paths.
• Preserve result-only output, distinct output, repeated output in later turns, held-turn handoff, orphan lanes, and lagged-idle behavior.

Validation

Live end-to-end verification

Ran the built adapter as an ACP subprocess using the real local Claude OAuth login, created a real ACP session, and sent /context through session/prompt.

Before the final fix:

agent_message_chunk count: 2
lengths: 2268, 2270
Context Usage heading count: 2

After the fix:

agent_message_chunk count: 1
length: 2268
sha256: 605f8d220d1a0f628d05c1128c4310f6ce0b8786d7a024928a51ca8e1168de2e
Context Usage heading count: 1
stopReason: end_turn

Automated verification

• Focused Vitest selection: 36 passed.
• npm run build: passed.
• npm run lint: passed.
• npx prettier --check src/acp-agent.ts src/tests/acp-agent.test.ts: passed.
• npm run test:run: 687 passed, 20 skipped, and the same 6 pre-existing Windows path-separator assertion failures (src/main.ts vs src\main.ts); no new failures.

Fixes #948