feat(shared): add json-cache utility for generic JSON file read/write

[iyoda]

Summary

Add a generic json-cache utility (readJsonFile / writeJsonFile) that encapsulates the common pattern of reading/writing JSON files with proper error handling and optional directory creation.

Changes

• New: src/shared/json-cache.ts (23 lines) — readJsonFile<T>() and writeJsonFile()
• New: src/shared/json-cache.test.ts (223 lines) — 13 comprehensive tests

API

readJsonFile<T>(path: string): T | null           // Returns null on missing/invalid
writeJsonFile(path: string, data: unknown, opts?)  // opts.ensureDir auto-creates parent

Verification

• bun run typecheck ✅
• bun test ✅ (2693 pass, 0 fail)
• bun run build ✅

PR Stack

This is PR 5 of 9 in the code deduplication refactor series. Depends on #1855. This PR adds the utility; the next PR (6) applies it to existing consumers.

#	PR	Description
0	#1852	Delete dead code in modules/
2	#1853	Consolidate formatDuration (4→1)
3	#1854	Consolidate getMessageDir (7→1)
4	#1855	Unify fuzzyMatchModel
5	This PR	Add json-cache utility
6	(next)	Apply json-cache to consumers
7		Add ensure-directory utility
8		Apply ensure-directory to production
9		Consolidate ToolContextWithMetadata

---

Summary by cubic

Adds a shared json-cache utility to safely read/write JSON files with optional directory creation, and consolidates duplicate helpers while deleting dead background-task modules. This standardizes common behavior and trims unused code.

• Refactors
  • Centralized getMessageDir in shared/session-utils; removed duplicates and updated imports across features/tools.
  • Centralized formatDuration in tools/background-task/time-format; removed old copies and deleted the background-task/modules directory.
  • Unified fuzzyMatchModel and normalizeModelName in model-name-matcher, with re-exports from model-availability for backward compatibility.

^{Written for commit 3e976bd. Summary will update on new commits.}

[cubic-dev-ai]

1 issue found across 37 files

Confidence score: 2/5

• High risk: package.json declares a self-dependency (oh-my-opencode depends on itself), which is very likely to break installs at runtime.
• This is a concrete, user-facing failure path, so merge confidence is low until the circular dependency is removed.
• Pay close attention to package.json - remove the self-dependency to avoid install failures.

Prompt for AI agents (all issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="package.json">

<violation number="1" location="package.json:65">
P0: Package has a self-dependency (oh-my-opencode depends on itself) which creates a circular dependency. This will cause installation failures.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

[cubic-dev-ai]

P0: Package has a self-dependency (oh-my-opencode depends on itself) which creates a circular dependency. This will cause installation failures.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At package.json, line 65:

<comment>Package has a self-dependency (oh-my-opencode depends on itself) which creates a circular dependency. This will cause installation failures.</comment>

<file context>
@@ -62,6 +62,7 @@
     "detect-libc": "^2.0.0",
     "js-yaml": "^4.1.1",
     "jsonc-parser": "^3.3.1",
+    "oh-my-opencode": "^3.5.5",
     "picocolors": "^1.1.1",
     "picomatch": "^4.0.2",
</file context>