fix(session): sanitize part IDs after plugin hooks

[CybLow]

Issue for this PR

Closes #18780

Type of change

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

What does this PR do?

Since v1.2.25 (#16966), all part IDs must start with "prt" (enforced by PartID.zod = z.string().startsWith("prt")). The createUserMessage() function in prompt.ts correctly generates compliant IDs via the assign() function. However, it then calls Plugin.trigger("chat.message", ..., { message: info, parts }), passing the parts array by reference to plugin hooks.

Plugins like opencode-supermemory push new parts into this array with non-compliant IDs (e.g., supermemory-nudge-*, supermemory-context-*). When Session.updatePart() is called afterwards, fn(MessageV2.Part, ...) runs PartID.zod.parse() and throws a ZodError, crashing the session.

This fix adds a sanitization loop after Plugin.trigger("chat.message") returns: any part with a missing or non-"prt" prefixed ID gets reassigned a valid PartID.ascending(). This protects the core against misbehaving plugins without breaking any existing behavior — parts that already have valid IDs are left untouched.

How did you verify your code works?

1. Identified the crash by tracing the stack from fn() in util/fn.ts through Session.updatePart() back to createUserMessage()
2. Confirmed that opencode-supermemory plugin injects parts with supermemory-nudge-* and supermemory-context-* IDs at dist/index.js:14548,14582
3. Verified locally that after patching, messages send without the ZodError when the plugin is active

Screenshots / recordings

Not a UI change.

Checklist

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

[github-actions]

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[github-actions]

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[rekram1-node]

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