Summary

Adapt Claude Opus 5 support onto Scient-owned provider, model-capability, discovery, and composer seams.

• keep Claude Opus 4.8 as the default
• expose Opus 5 only when the exact configured Claude executable reports version 2.1.219 or newer
• preserve native [1m] context suffixes and Scient's static ultracode capability
• normalize persisted and outgoing model options against runtime-aware capabilities
• scope model and subagent discovery to the configured executable and working directory
• isolate agent catalog cache and in-flight discovery by exact {cwd,binaryPath}

Donor provenance and disposition

Selected bounded concepts:

• Synara 83b685234b2c474ea4d9a6ce593ac730ca95f8f7: Adapt the Opus 5 capability/version-gating concept; do not import donor lifecycle, persistence, identity, or broad provider architecture.
• T3 Code 41a430a88e8dde9c428f59d54dd328aa6a66a8fd: Reimplement the static Opus 5 capability facts on Scient-owned seams; do not import T3 product or architecture assumptions.

The complete newly observed awareness ranges were dispositioned separately during the steward run (Synara 14 commits through 3f66f8ee5b1e5d8aa682029b31b4b89b797a5e7f; T3 5 commits through 38cfc25e5422e468303f2010f639cf3de9ad89ba). Other lanes were rejected, deferred, or retained as future design/reliability lessons. Synara's final 3f66f8e release-metadata and donor-branded What's New content were rejected for direct intake because Scient already owns curated, identity-safe release notes. This PR does not advance either durable review boundary or integration base.

Exact candidate

• Base: 341055d518cafabaa71f6a4c9a4ea42a9dc8cb8d
• Candidate: 3249ab8732669cd53499d27a6115db76840804cd
• Branch: maintenance/upstream-opus5-20260725

Protected lanes

No migrations, persistent-data changes, credential/session policy changes, approval or permission broadening, dependency changes, updater controls, release authority, telemetry, or Scient identity changes. Configured executable selection is respected for both model and subagent discovery. Temporary discovery uses strict empty MCP isolation, no persisted session, managed-executable updater disabled, and closes in finally.

Verification

Exact-head local certification:

• bun run scient:upstream-check --intake
• brand/identity checks
• format verification
• lint (existing warnings only)
• typecheck
• full bun run test
• desktop/web build
• release smoke
• focused Claude adapter: 98/98
• focused shared model capability suite: 93/93
• focused web discovery/prefetch: 15/15
• stable browser: 55 files, 355 passed, 19 skipped
• git diff --check
• clean worktree after tests

A prior candidate also passed the cross-repository Scient agent smoke against scient-agent 709a26002c697f06cbaebeb8fac40e87de0ab6b3; subsequent changes are confined to Claude provider/web discovery and do not alter the shared OpenCode agent contract.

Independent review

Exactly three read-only reviews covered:

1. correctness, reliability, concurrency, lifecycle, performance, and regressions
2. security, privacy, data loss, credentials, sessions, permissions, updater/release safety
3. architecture, maintainability, ownership, lineage, product design, accessibility, and evidence sufficiency

Review findings were resolved before publication, including runtime capability lookup, CLI version gating, composer normalization, [1m] preservation, configured-binary discovery, and executable/cwd-scoped agent caching. All three reviewers recertified exact candidate 3249ab8 with no remaining P0-P2 findings.

Manual evidence and limitations

An isolated actual-app run verified the unauthenticated Claude recovery state. The credentialed positive Opus 5 row and live send path were not exercised because the review did not use production credentials; deterministic component/browser/adapter tests cover availability, fallback, switching, and option normalization.

Rollback and dependencies

Rollback is one revert of 3249ab8732669cd53499d27a6115db76840804cd. There is no migration or cleanup step. No cross-repository PR dependency and no checkpoint/evidence PR.

This PR must remain draft until hosted CI is classified. It is not release authorization.