Reddit user SSShken's controlled second-account comparison claims Claude Code's machine-level plugins, skills, and MCP servers in the home directory inject instructions into every session regardless of account, so account-level isolation does not reset the agent's instruction surface; independent reproduction or an Anthropic response resolves it.

state: seedheat: lowuncertainty: mediumconvergesscott: highagent-harnesses claude-code context-injection

What is this?

A Reddit user (SSShken) reports that buying a second Claude account to get a clean, fair Claude Code comparison against Cursor and Codex failed: plugins, skills, and MCP servers configured at the machine level (the home-directory ~/.claude surface) inject instructions into every session regardless of which account is signed in, so account switching is not an isolation boundary. The supplied snippets independently corroborate the mechanism — Anthropic's own issue tracker documents marketplace MCP instructions consuming 30–55% of fresh-session context before any user input (claude-code #48680) and the Agent SDK's `settingSources: []` 'isolation mode' still loading user-level MCP servers and skills at ~35K tokens (#30304), while security write-ups confirm the global scope applies to every session regardless of directory and treat SKILL.md/MCP prose as live instruction channels. The snippets do not include the original post itself, so the poster's specific measurements rest on a single testimony source; and the framing is contested even in the tracker — machine-scoped config is documented behavior, while unconditional instruction injection is filed as a bug requiring a separate fix.

Why it matters to Scott

Converges with his isolation doctrine — principal-cell/runtime-containment already argue account identity is not an isolation boundary, and a harness he drives daily now demonstrates it: the real boundary is ~/.claude, so a 'fresh account' benchmark is still contaminated. The corroborating tracker numbers (marketplace MCP instructions consuming 30–55% of fresh sessions; ~35K tokens even with settingSources: []) are dated receipts for his context-bloat and code-execution-beats-MCP arguments — and they warn that his own cross-harness A/Bs (Claude Code vs Codex vs OpenCode) must pin the machine-level config surface or they benchmark the wrong unit.

dev:technology.claude-codeip:concept.principal-cellip:concept.context-bloatip:source.context-engineering-why-building-ai-agents-feels-like-programming-on-a-vic-20-again-ebookip:concept.model-plus-harness-benchmark-unitip:source.why-code-execution-beats-mcpradar:claude-code-nested-instruction-loadingradar:claude-projects-account-memory-defaultradar:claude-code-remote-attribution-injectionradar:blocks-mcp-cli-context-cost

queries asked of Scott's wikis

claude code settings precedence harness configuration
agent session baseline context overhead token budget
coding agent comparison methodology clean environment
instruction injection surface skills CLAUDE.md SKILL.md
agent isolation machine vs account vs project scope
MCP server instructions loaded every session startup

Measured heat

now 0 pts/hpeak 2 pts/hcomments 0/hpeers p0momentum: steady2 platformsage 482h

points/hour across evidence · reading as of 2026-10-12 02:59:37.977291+11:00 · deterministic, not a model opinion

How the heat travelled

09-21 14:00	⭐ origin echo-reconstructed	The origin is the author's own long-form X article — the "full writeup with screenshots, the exact spec I gave all three, and the numbers" ( Artem Horobchenko (@SSShken) on x (echo) · attributed from reddit.post.1wv51i1	—
10-01 17:06	first on r/ClaudeAI · published · +243.1h	I bought a second Claude account to test it fairly against Cursor and Codex, and it still wasn't clean SSShken	—
10-01 17:06	amplified on r/ClaudeAI 👑	reddit.post.1wv51i1 SSShken	peak 3 · 5 comments · 99% of case engagement
10-01 18:20	our radar first saw it · +244.3h	discovery anchor: reddit.post.1wv51i1	—

pace: p42 vs 1032 stories at the 336h mark (now 482h old) — ahead of agent-memory-add-search-evaluation (1.2x), behind agenticos-self-hosted-governance (0.9x)

Evidence (2) — ⭐ canonical anchor

source	object	author	score	comments
🟠 reddit	I bought a second Claude account to test it fairly against Cursor and Codex, and it still wasn't clean ClaudeAI	SSShken	3	5
🟧 echo.x ⭐	The origin is the author's own long-form X article — the "full writeup with screenshots, the exact spec I gave all three, and the numbers" (	Artem Horobchenko (@SSShken)	—	—

Interpretation history

2026-10-01T19:04:36Z
origin walked (opencode/cheap-glm, conf 0.85): anchor reddit.post.1wv51i1 -> echo.x.a4655ed053 by Artem Horobchenko (@SSShken)
2026-10-01T18:51:06Z
grounded: converges/high — Converges with his isolation doctrine — principal-cell/runtime-containment already argue account identity is not an isolation boundary, and a harness he drives
2026-10-01T18:42:40Z
case created — Reproducible controlled-experiment claim about a distinct isolation failure (machine-level config surviving account resets) that no open case covers — nested-instruction-loading is a different mechanism.

Decision trace

10-02 05:04promote_anchororigin walk conf 0.85
10-02 04:51groundConverges with his isolation doctrine — principal-cell/runtime-containment already argue account identity is not an isolation boundary, and a harness he drives daily now demonstrates it: the real boun
10-02 04:42createReproducible controlled-experiment claim about a distinct isolation failure (machine-level config surviving account resets) that no open case covers — nested-instruction-loading is a different mechani