fix(tui): stop session-switch crash from object-valued tool fields in <text>

[devinoldenburg]

Summary

Fixes #26. The TUI crashed with a fatal TextNodeRenderable only accepts strings, TextNodeRenderable instances, or StyledText instances when switching into a session whose parts contained tool input/metadata, diagnostic, or error fields that were not strings. It reproduced with and without a PDF attachment, because the trigger is the tool/diagnostic render path, not attachments.

Cause / Investigation

• opentui core (@opentui/core) TextRenderable.add() accepts only string, TextNodeRenderable, or StyledText. Any other child (plain object, array, store proxy, Date, etc.) throws the reported error. In the @opentui/solid reconciler, insertExpression's final else branch passes such values straight to parent.add().
• The live session renderer packages/codeplane/src/tui/routes/session/index.tsx interpolated several unknown/any-typed values directly as <text> children:
  • tool state.input.{command,pattern,url,query,name} (typed unknown; raw/partial/streamed tool-call JSON can be an object/array, not a string)
  • diagnostic.message (Record<string, any>)
  • message.error.data.message (unknown for MessageOutputLengthError)
• On session switch, syncSessionData in context/sync.tsx reloads all messages/parts via reconcile, and SolidJS re-renders them. An object child then reaches TextNodeRenderable.add() and takes down the whole TUI.
• The sibling renderers feature-plugins/system/session-v2.tsx (stringValue()) and routes/session/permission.tsx (typeof === "string" guards) already guard these exact fields; the live routes/session/index.tsx did not. That asymmetry was the bug.

Changes

• packages/codeplane/src/tui/util/text-value.ts (new): textValue() always returns a string — passes strings through, renders nullish as "", coerces scalars (number/bigint/boolean), and JSON-serializes objects/arrays with a defensive fallback that never throws.
• packages/codeplane/src/tui/routes/session/index.tsx: wrap every at-risk <text> interpolation with textValue(...) — Shell command (block + inline), Glob/Grep pattern, WebFetch url, WebSearch query, Skill name, Diagnostics message, and the assistant error data.message.
• packages/codeplane/test/tui/text-value.test.ts (new): regression coverage asserting textValue always returns a string for strings, nullish, scalars, objects/arrays (the crash case), and hostile inputs (circular refs, symbols, throwing toJSON).

Verification

• bun --cwd packages/codeplane test test/tui/text-value.test.ts — 5 pass, 0 fail
• bun turbo typecheck --filter=codeplane — 0 errors
• bun lint — 0 errors (warnings only)

Note: test/tui/dispatch*.test.ts and auth-helper.test.ts fail in this environment both with and without this change (pre-existing global-state flakes per AGENTS.md); they are unrelated to this fix.

[devinoldenburg]

Review Notes

Verdict: APPROVED — ready to merge

What this does

Fixes a TUI crash where switching into a session with non-string tool input/metadata fields (objects, arrays, etc.) would throw in TextNodeRenderable.add() and bring down the entire TUI.

Review

• packages/codeplane/src/tui/util/text-value.ts — clean, defensive, well-commented. The fallback chain (string → nullish → scalars → JSON.stringify → String()) is correct and the hostile-input test confirms it never throws.
• packages/codeplane/src/tui/routes/session/index.tsx — all 9 interception points are the exact fields known to carry unknown-typed values from tool calls. The change is minimal and surgical.
• packages/codeplane/test/tui/text-value.test.ts — solid regression coverage including circular refs, symbols, Maps, and throwing toJSON(). Good.

No issues found

This is a low-risk bugfix with good test coverage. Safe to merge.