fix(server): OpenCode 2 threads get T3 Code's MCP tools

[nkoynov]

Problem

OpenCode 2 threads and delegated OpenCode 2 children never see T3's MCP tools. The adapter registers the server as t3-code-<threadId>, which is 96 characters for a V2 project thread and over 100 for a delegated child. OpenCode skips every tool of a server whose name is over 64 characters (its tool-namespace limit; only its log says so), and its router 404s PUT /api/experimental/mcp/:server for a name over 100, so T3 logs "Could not add T3 Code's MCP server to OpenCode." Fixes #16140.

Change

t3McpServerName keeps a name that fits in 64 characters and otherwise uses t3-code- plus the first 16 hex characters of the thread id's SHA-256 (24 characters). The name is deterministic, so every turn of a thread registers the same server. The session's t3-code-* deny and <name>_* allow rules, mcp.add and mcp.remove all go through this name (removal uses the stored state.mcp.name), so each thread is still limited to its own server. Hashed names have a fixed length, so one thread's <name>_* allow rule can't match another thread's tools.

Scope and approval

This is a very small, focused fix for an obvious bug, and it qualifies for the exception without a prior discussion: one helper in the OpenCode 2 adapter plus tests, no contract, client or behaviour change beyond OpenCode receiving a name it accepts. The intended behaviour is already established, because the adapter registers the server for exactly this purpose. Issue #16140 has the full report. Same class of bug as #8860 (long V2 ids over a 100-character route limit, fixed in T3's own routes by #8898). #15736 also goes through prepareTurn/mcp.add, but it is a different bug.

Verification

Focused tests (in OpenCode2AdapterV2.test.ts):

• registers a long thread id's MCP server under a name OpenCode accepts replays a delegated child id that used to produce a 120-character name. It checks that mcp.add, the session's allow rule and mcp.remove all use t3-code-aa73fa1e03099934.
• names each thread's MCP server within OpenCode's limits, one name per thread checks real-format project and delegated ids: each name is 64 characters or fewer and valid, ids that differ only at the end get different names, a name is stable across calls, and a short id keeps its readable name.
• Against main's adapter, both new tests fail. The first fails because the adapter rewrites the session rules with the 120-character t3-code-thread_delegated-task_…_* allow rule; the second with expected 't3-code-thread_project_ce04e4e2-…' to match /^t3-code-[A-Za-z0-9_-]{1,56}$/.

vp test run apps/server/src/orchestration-v2/Adapters/OpenCode2AdapterV2.test.ts apps/server/src/orchestration-v2/OpenCode2OrchestratorV2.integration.test.ts
  Test Files  2 passed (2)   Tests  96 passed (96)
vp lint <2 files>          Found 0 warnings and 0 errors.
vp fmt --check <2 files>   All matched files use the correct format.
vp run --filter t3 typecheck   exit 0

Live, with T3 from source (node apps/server/src/bin.ts serve, scratch home), OpenCode 2.0.22 spawned by T3, no OpenCode plugins, and the free opencode/big-pickle model:

Case	main @ e22c880	this PR
Project thread, Code Mode search({query: "t3_thread_configuration"}) on turn 2	[]; 72 Invalid tool namespace errors in opencode.log	tools["t3-code-5f396b4d3be75e9c"].t3_thread_configuration, … ; 0 errors
Claude parent → delegate_task → OpenCode child that calls t3_thread_configuration	CHILD_NO_T3_TOOLS; T3 logs 404 PUT …/api/experimental/mcp/t3-code-thread_delegated-task_command_3Amcp_3A7ca20ace-…	child returns its own id thread:delegated-task:command%3Amcp%3A2124c561-…%3Adelegate-task%3Aoc-child-check-1; no warning
OpenCode parent (Code Mode delegate_task) → OpenCode child	parent has no T3 tools	child returns its own thread id

With cursor-opencode-provider 0.8.0 and cursor/claude-opus-5-5-1m, the model called t3-code-6fb4b99c8f0e4cda_t3_thread_configuration and got its own thread id back. On nightly 0.0.46-nightly.20261004.2648, the same model and plugin found no T3 tools, and opencode.log had the same 72 Invalid tool namespace errors.

Rebased onto main @ 3e6b450 before opening: the same focused tests (96/96), lint and vp run --filter t3 typecheck pass there.

Not covered by this PR: on a thread's first turn the tools can still be missing, because OpenCode registers them about 100 ms after mcp.add returns (debounced) and the first step's catalog is already taken. That is a separate race (reported as #16141, the OpenCode analogue of #13437), and these tables use turn 2 to keep the cases apart. Not tested: an external serverUrl (T3 adds no MCP server there), Windows.

Model: Claude Opus 5.5 (1M). Harness: Claude Code in T3 Code.

[macroscopeapp]

Approvability

Verdict: Approved at 3267045

Macroscope's review found this PR approvable — This is a small, self-contained fix for OpenCode 2 MCP servers whose long thread-derived names exceeded provider limits. Existing short names remain unchanged, long names become deterministic and bounded, and registration, permission matching, cleanup, and focused tests all use the same naming function.

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📥 Commits

Reviewing files that changed from the base of the PR and between 3e6b450 and 3267045.

📒 Files selected for processing (2)

• apps/server/src/orchestration-v2/Adapters/OpenCode2AdapterV2.test.ts
• apps/server/src/orchestration-v2/Adapters/OpenCode2AdapterV2.ts

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📝 Walkthrough

Walkthrough

The OpenCode 2 adapter now shortens generated MCP server names when sanitized thread IDs exceed 64 characters. Tests cover name generation and MCP server registration for a long thread ID.

Changes

OpenCode 2 MCP server names

Layer / File(s)	Summary
Bounded MCP name generation apps/server/src/orchestration-v2/Adapters/OpenCode2AdapterV2.ts	The exported t3McpServerName keeps sanitized names up to 64 characters. For longer names, it uses t3-code- plus the first 16 hexadecimal characters of the thread ID’s SHA-256 digest.
MCP registration replay and name tests apps/server/src/orchestration-v2/Adapters/OpenCode2AdapterV2.test.ts	Tests check registration before the prompt and removal when a long-ID thread unloads. They also check the generated name pattern, uniqueness, stability, and preservation of an existing short name.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix · Severity of issue fixed: Medium

Suggested reviewers: juliusmarminge

Merge Risk: ⚪ Minimal · up to 32670

No actionable merge-blocking issue is identified for the OpenCode 2 MCP naming change. It is mergeable after normal checks.

Architecture Summary

Architecture risk: 🔵 Low · up to 32670

The change affects 1 system.

Changed systems: apps/server

Architecture concerns
No architecture-level concerns identified.

Review details

Systems and components

• observed — apps/server (service) was modified; 2 changed files map to changed impact.

Before / after behavior

• observed — Modified behavior in apps/server/src/orchestration-v2/Adapters/OpenCode2AdapterV2.test.ts: The test now imports t3McpServerName from OpenCode2AdapterV2.ts alongside OPENCODE_2_STILL_STOPPING.
• observed — Modified behavior in apps/server/src/orchestration-v2/Adapters/OpenCode2AdapterV2.test.ts: Adds a replay test for resuming a long-ID thread with its MCP session registered under t3-code-aa73fa1e03099934; it verifies the server is added before the prompt, removed when the thread unloads, and the turn completes.
• observed — Modified behavior in apps/server/src/orchestration-v2/Adapters/OpenCode2AdapterV2.test.ts: Adds assertions that names generated for several thread IDs fit t3-code-[A-Za-z0-9_-]{1,56}, are unique, and stable across calls, while the existing short thread ID remains readable.
• observed — Modified behavior in apps/server/src/orchestration-v2/Adapters/OpenCode2AdapterV2.ts: The file adds the Node crypto import used to digest long MCP server names.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Issue [#16140] requires OpenCode 2 project threads and delegated children to access T3 MCP tools. The adapter keeps sanitized names at 64 characters or fewer and uses a deterministic 16-hex SHA-256 su…
Out of Scope Changes check	✅ Passed	The production change only shortens OpenCode 2 MCP server names. The added tests cover the naming behavior and its use during registration and removal. No unrelated changes appear in the pull request …
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 2…
Title check	✅ Passed	The title clearly states the main change: OpenCode 2 threads can access T3 Code's MCP tools.
Description check	✅ Passed	The description covers the problem, change, scope and approval rationale, and detailed verification. It also identifies limitations and untested cases.

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