feat(opencode): add db doctor and repair commands

[pascalandr]

Issue for this PR

Related issues (does not automatically close): #29908, #31204, #19191, #29581, #31597, #23594, #30157, #14970, #24780.

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Adds native database health commands for local OpenCode SQLite databases:

• opencode db doctor and opencode db doctor --json
• opencode db repair --dry-run and opencode db repair --apply

The commands inspect local OpenCode SQLite databases directly. They diagnose/repair rows by comparing persisted data shapes against the invariants required by the OpenCode binary currently running the command.

The supported repair catalog is exported from @opencode-ai/core/database/health as SUPPORTED_REPAIRS and is included in doctor / repair --dry-run JSON output. Each catalog entry declares the target OpenCode version/invariant, known target migration when applicable, source evidence if known, repair behavior, and safety constraints. The report also includes a compatibility block with the current binary version, expected migrations for that binary, applied DB migrations, and observed session.version distribution.

Supported repair catalog (for now)

• part_legacy_id_prefix: renames part_<suffix> IDs to prt_<suffix> only when the target ID does not already exist. This fixes the observed load failure: Expected a string starting with "prt", got "part_..." at [0]["parts"][0]["id"].
• assistant_message_missing_agent: copies assistant session_message.data.mode to data.agent with original-JSON precondition checks.
• session_agent_missing: fills session.agent only when one unambiguous value can be derived from assistant or agent-switched messages.
• session_model_missing: fills session.model only when one unambiguous model object can be derived from assistant or model-switched messages.
• session_path_missing: fills session.path from the same row's non-empty session.directory.
• message_assistant_missing_parent: fills missing assistant parentID from the immediately preceding message in the same session.
• message_user_missing_agent: fills missing user agent only when one unambiguous agent is derivable.
• message_user_missing_model: fills missing user model only when one unambiguous model is derivable.
• part_step_finish_missing_reason: fills missing step-finish.reason with stop.
• part_compaction_missing_auto: fills missing compaction.auto with false.
• part_tool_completed_missing_metadata: fills missing completed-tool state.metadata with {}.
• part_tool_completed_missing_title: fills missing completed-tool state.title from data.tool only when present.
• part_tool_completed_missing_time: fills missing completed-tool state.time.start/end from the part row timestamp while preserving any existing start/end value.

How did you verify your code works?

I manually validated the tool against several real local user database and confirmed it repaired the targeted damaged session rows that caused session loading failures in Codenomad.

Screenshots / recordings

Not a UI change.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

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