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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Move simulatorPlatform out of sessionDefaults into an internal cache","articleBody":"## Problem\n\n`sessionDefaults.simulatorPlatform` is declared as a session default (see `src/utils/session-defaults-schema.ts:35-38`, described as \"Cached inferred simulator platform\"), but it does not behave like one.\n\nSession defaults are meant to be values an agent sets to influence tool calls. `simulatorPlatform` violates that contract:\n\n- It is written automatically by `src/utils/simulator-defaults-refresh.ts` (lines 80, 87) as a side effect of resolving a simulator — not by an agent.\n- It is keyed to another default (`simulatorId` / `simulatorName`) and only trusted when those still match (`src/utils/infer-platform.ts:113-139`, `resolveCachedPlatform`).\n- Its sole consumer is `infer-platform.ts`, which uses it to skip a `simctl list` round-trip.\n\nIn other words, it is internal cache state surfaced through the agent-facing session-defaults schema. Agents that read or write `sessionDefaults` see a field they should not be touching, and any code that legitimately wants to set a project's \"platform\" preference (e.g. the setup wizard in #365) gets pulled into caching semantics it does not want.\n\n## Proposed direction\n\nTwo reasonable options:\n\n1. **Move it to a separate internal cache** that is not part of `sessionDefaults` and is not exposed via `session_set_defaults` / `session_show_defaults` / `session_clear_defaults`. `infer-platform.ts` and `simulator-defaults-refresh.ts` become the only readers/writers.\n2. **Drop the cache entirely** and re-derive the simulator platform on demand from `simulatorId` via `simctl list`. Costs one extra lookup per fresh session; removes a whole class of staleness bugs.\n\nOption 1 preserves the perf optimisation; option 2 is simpler. Either is fine — the key constraint is that `simulatorPlatform` should not be in `sessionDefaults`.\n\n## Out of scope\n\n- `sessionDefaults.platform` — that one is a legitimate agent-controllable default for device tools and should stay.\n- The setup-wizard layering issue surfaced in #365 — that PR should stop writing to either field; this issue is the follow-up cleanup.\n\n## Affected files (current state)\n\n- `src/utils/session-defaults-schema.ts` — declares the field\n- `src/utils/simulator-defaults-refresh.ts` — writer\n- `src/utils/infer-platform.ts` — reader\n- `src/mcp/tools/session-management/session_*.ts` — surfaces it to agents\n- `src/utils/renderers/domain-result-text.ts`, `src/types/domain-results.ts` — render/type plumbing","author":{"url":"https://github.com/cameroncooke","@type":"Person","name":"cameroncooke"},"datePublished":"2026-04-26T20:08:38.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":4},"url":"https://github.com/366/XcodeBuildMCP/issues/366"}