Non-ASCII IDNA Label Separator Inside the Host of a Fetch-Tool URL Argument

Detects a tool call whose URL-typed argument (url, uri, target_url, href, link, src, endpoint, location, website, site, page, target) or host-typed argument (host, hostname, domain, *_host, server_name) carries one of five separator characters: the three that IDNA / UTS #46 mapping turns into an ordinary dot -- U+3002 IDEOGRAPHIC FULL STOP, U+FF0E FULLWIDTH FULL STOP, U+FF61 HALFWIDTH IDEOGRAPHIC FULL STOP -- plus the two look-alike separators U+2024 ONE DOT LEADER and U+FE52 SMALL FULL STOP, INSIDE THE HOST COMPONENT (after '//' and before the first '/', '?' or '#'), and immediately followed by another hostname label, a path/query/fragment delimiter, or a ':port'. Examples: https://evil。com/page, https://evil.com．/page, https://internal-admin。corp。example/api/keys. Mined from CVE-2026-107288 (Pydantic AI web_fetch_tool and the WebFetch local fallback, 1.77.0 up to 1.107.6 / 2.44.0): blocked_domains entries were compared with the URL hostname before either side was normalised to the form getaddrinfo resolves, so a model steered by injected content could spell a blocked host with a non-ASCII label separator and the application fetched it with its own privileges (SSRF). The detection is not bound to any domain: a hostname has no legitimate reason to carry these characters in the serialized tool argument, because every conforming client folds them to '.' before resolution, so their presence is the signature of a string-level allow/block-list being dodged. The same shape defeats any agent fetch tool whose domain filter compares strings before IDNA mapping. BOTH ENCODINGS. The separator is matched as the literal character (what JSON.stringify emits) and as the JSON escape \u3002 / \uff0e / \uff61 / \u2024 / \ufe52 (what Python json.dumps emits with its default ensure_ascii=True), so a Python-side hook log is covered as well. WHY A KEYED ARGUMENT IS REQUIRED. Chinese and Japanese prose routinely ends a sentence with U+3002 directly after a URL ("請參考 https://example.com。謝謝"), and mixed-language text can put an ASCII word straight after that full stop ("https://example.com。GitHub 上也有說明"). The second form is indistinguishable by pattern from https://evil。com, so the rule only reads a value that sits behind a quoted URL/host argument key, where prose does not appear. A separator that is the LAST character of the value (the trailing full stop an extractor copies from a sentence) is also excluded. HOST-TYPED ARGUMENTS ARE READ STRICTLY. Keys such as domain, host or server_name are also used for free text (a topic domain, a podcast host, a display name), so for those keys the WHOLE value must be ASCII hostname shaped -- [a-z0-9.-] labels, the separator, more labels, an optional ':port' -- and must run to the closing quote. CJK prose in such a field (醫療。AI 應用, 王小明。Guest: Amy, 東京サーバー。Tokyo-1) is therefore not read. SCOPE AND LIMITS, stated honestly. (1) Not covered: case variation (EVIL.COM) and a plain trailing root dot (evil.com.) -- they are the same bytes as ordinary URLs. (2) Not covered by this rule: fullwidth-letter hostnames with only ASCII dots (ｅｖｉｌ.ｃｏｍ) -- ATR-2026-00444 sees those; cloud-metadata hosts written with separators also hit ATR-2026-00013. (3) Not covered: a bare URL in prose or in a non-URL argument (a chat message, a document body, a search query); that form is undecidable from Chinese punctuation. A URL passed under a key outside the lists above (q, query, text, content, input) is a known gap. (4) Not covered: punycode (xn--) spellings of a blocked IDN, percent-encoded host bytes, and a trailing separator that ends the value. (5) A security test suite or advisory that reproduces the serialized call verbatim will match. RE2 PORTABILITY. Both conditions are written for RE2-family engines (Go regexp, Rust regex) as well as JavaScript and Python re: the five separator characters and the fullwidth letter/digit ranges are written as literal characters rather than \\uXXXX escapes (which RE2 spells \\x{XXXX} and JS without the u flag does not), there is no lookahead or lookbehind, and every repeat bound is at most 253. The "not the last character of the value" exclusion is expressed by requiring a following label character, delimiter or ':port' after the separator instead of a negative lookahead, so the matched behaviour is unchanged.

Response Actions

References

1. 01

   A quoted URL-typed argument whose HOST component (between '//' and the first '/', '?' or '#') contains an IDNA label separator (U+3002, U+FF0E, U+FF61) or look-alike dot (U+2024, U+FE52), literal or JSON-escaped, followed by another label, a delimiter or a port -- the CVE-2026-107288 blocked_domains bypass shape.

   field: tool_argsop: regex
2. 02

   The same separator inside a bare host-typed argument (host / hostname / domain / *_host / server_name) that a tool resolves directly -- the scheme-less form of the same normalisation bypass. The whole value must be an ASCII hostname (labels, separators, optional :port) running to the closing quote, so CJK free text in such a field is not read.

   field: tool_argsop: regex

Attack Examples (Rule Triggers)

1. {"tool_name":"web_fetch","arguments":{"url":"https://evil。com/page"}}

2. {"tool_name":"web_fetch","arguments":{"url":"https://evil.com．/page"}}

3. {"tool_name":"web_fetch","arguments":{"url":"https://evil.com｡/page"}}

4. {"tool_name":"web_fetch","arguments":{"url":"https://evil.com․/page"}}

5. {"tool_name":"web_fetch","arguments":{"url":"https://internal-admin。corp。example/api/keys"}}

6. {"tool_name":"web_fetch","arguments":{"url":"https://evil\u3002com/page"}}

7. {"tool_name":"http_get","arguments":{"target_url":"http://intranet﹒corp:8443/admin"}}

8. {"tool_name":"dns_lookup","arguments":{"hostname":"internal-admin．corp．example"}}

9. {"tool_name":"connect_db","arguments":{"db_host":"pg-primary。internal:5432"}}

10. {"tool_name":"dns_lookup","arguments":{"hostname":"internal-admin\u3002corp\u3002example"}}

11. {"tool_name":"crawl","arguments":{"website":"https://evil。com/"}}

12. {"tool_name":"web_fetch","arguments":{"url":"https://evil。ｃｏｍ/page"}}

13. {"tool_name":"dns_lookup","arguments":{"host":"metadata﹒internal"}}

Real-world attack payloads, sanitized and versioned alongside the rule as regression tests — so a future revision can't silently stop catching them.

Benign Examples (Rule Doesn't Trigger)

1. BENIGN TWIN: ordinary web_fetch call on the same tool and argument

   {"tool_name":"web_fetch","arguments":{"url":"https://example.com/page"}}

2. BENIGN TWIN: a punycode IDN host, the legitimate ASCII-compatible form

   {"tool_name":"web_fetch","arguments":{"url":"https://xn--bcher-kva.example/page"}}

3. BENIGN TWIN: a native Unicode IDN host with ordinary ASCII dots

   {"tool_name":"web_fetch","arguments":{"url":"https://bücher.example/page"}}

4. BENIGN TWIN: U+3002 in the PATH followed by ASCII -- outside the host component

   {"tool_name":"web_fetch","arguments":{"url":"https://zh.wikipedia.org/wiki/句號。Wiki"}}

5. BENIGN TWIN: U+3002 in the query string

   {"tool_name":"web_fetch","arguments":{"url":"https://www.google.com/search?q=台北。weather"}}

6. BENIGN TWIN: a URL extracted from a Chinese sentence with its trailing full stop -- the separator ends the value

   {"tool_name":"web_fetch","arguments":{"url":"https://example.com。"}}

7. BENIGN TWIN: Chinese sentence-final full stop right after a URL, followed by CJK text

   {"tool_name":"send_message","arguments":{"text":"請參考 https://example.com。謝謝"}}

8. BENIGN TWIN: full stop followed by an ASCII word in prose -- not a URL-typed argument, so not read

   {"tool_name":"send_message","arguments":{"text":"網址是 https://github.com。GitHub 上也有 CI/CD 說明"}}

9. Ordinary host-typed argument

   {"tool_name":"dns_lookup","arguments":{"hostname":"api.example.com"}}

10. Raw Chinese prose with a URL and a sentence-final full stop

    請參考 https://example.com。謝謝

11. Python-escaped Chinese path ending in an escaped U+3002 -- outside the host

    {"tool_name":"web_fetch","arguments":{"url":"https://example.com/\u8def\u5f91\u3002"}}

12. BENIGN TWIN: domain key holding a CJK topic phrase with a full stop followed by ASCII (round-1 FP)

    {"tool_name":"classify","arguments":{"domain":"醫療。AI 應用"}}

13. BENIGN TWIN: host key meaning a podcast host, CJK name then an ASCII word (round-1 FP)

    {"tool_name":"podcast_note","arguments":{"host":"王小明。Guest: Amy"}}

14. BENIGN TWIN: server_name display label in Japanese followed by an ASCII tag (round-1 FP)

    {"tool_name":"create_vm","arguments":{"server_name":"東京サーバー。Tokyo-1"}}

15. BENIGN TWIN: *_host key holding a Japanese label, not a hostname (round-1 FP)

    {"tool_name":"connect","arguments":{"db_host":"本番DB。Primary"}}

16. BENIGN TWIN: host-typed value whose separator is the last character (copied sentence stop)

    {"tool_name":"set_config","arguments":{"domain":"example.com。"}}

17. BENIGN TWIN: ordinary website argument with ASCII dots

    {"tool_name":"crawl","arguments":{"website":"https://example.com/about"}}

Known False Positive Contexts

• ▸Security test suites, CVE reproductions and advisories that quote the serialized tool call verbatim (for example the upstream tests/test_ssrf.py fixtures) match -- same bytes as the attack.
• ▸A URL argument whose host was copied out of East Asian text together with a full stop AND has more host text after it (https://example.com。cn/...) matches. That value does not resolve as written by a strict parser and does resolve to a different host after IDNA folding, so it is reported deliberately.
• ▸A link / href / url field populated from scraped prose can carry a sentence-final full stop followed by an ASCII word, for example {"link":"https://t.co。Thanks"}. That value matches, because it is byte-for-byte the same shape as https://evil。com and cannot be told apart by pattern.
• ▸Not matched by design: a separator in the PATH, QUERY or FRAGMENT (https://zh.wikipedia.org/wiki/句號。, ?q=台北。天氣), a separator that is the last character of the value, punycode xn-- hosts, native IDN hosts such as bücher.example, and any URL that appears in prose or a non-URL argument.

title: "Non-ASCII IDNA Label Separator Inside the Host of a Fetch-Tool URL Argument"
id: ATR-2026-02866
rule_version: 1
status: experimental
description: >
  Detects a tool call whose URL-typed argument (url, uri, target_url, href,
  link, src, endpoint, location, website, site, page, target) or host-typed
  argument (host, hostname, domain, *_host, server_name) carries one of five
  separator characters: the three that IDNA / UTS #46 mapping turns into an
  ordinary dot -- U+3002 IDEOGRAPHIC FULL STOP, U+FF0E FULLWIDTH FULL STOP,
  U+FF61 HALFWIDTH IDEOGRAPHIC FULL STOP -- plus the two look-alike
  separators U+2024 ONE DOT LEADER and U+FE52 SMALL FULL STOP,
  INSIDE THE HOST COMPONENT (after '//' and before the first '/', '?' or '#'),
  and immediately followed by another hostname label, a path/query/fragment
  delimiter, or a ':port'. Examples: https://evil。com/page,
  https://evil.com．/page, https://internal-admin。corp。example/api/keys.

  Mined from CVE-2026-107288 (Pydantic AI web_fetch_tool and the WebFetch local
  fallback, 1.77.0 up to 1.107.6 / 2.44.0): blocked_domains entries were compared
  with the URL hostname before either side was normalised to the form
  getaddrinfo resolves, so a model steered by injected content could spell a
  blocked host with a non-ASCII label separator and the application fetched it
  with its own privileges (SSRF). The detection is not bound to any domain: a
  hostname has no legitimate reason to carry these characters in the
  serialized tool argument, because every conforming client folds them to '.'
  before resolution, so their presence is the signature of a string-level
  allow/block-list being dodged. The same shape defeats any agent fetch tool
  whose domain filter compares strings before IDNA mapping.

  BOTH ENCODINGS. The separator is matched as the literal character (what
  JSON.stringify emits) and as the JSON escape \u3002 / \uff0e / \uff61 /
  \u2024 / \ufe52 (what Python json.dumps emits with its default
  ensure_ascii=True), so a Python-side hook log is covered as well.

  WHY A KEYED ARGUMENT IS REQUIRED. Chinese and Japanese prose routinely ends a
  sentence with U+3002 directly after a URL ("請參考 https://example.com。謝謝"),
  and mixed-language text can put an ASCII word straight after that full stop
  ("https://example.com。GitHub 上也有說明"). The second form is
  indistinguishable by pattern from https://evil。com, so the rule only reads a
  value that sits behind a quoted URL/host argument key, where prose does not
  appear. A separator that is the LAST character of the value (the trailing
  full stop an extractor copies from a sentence) is also excluded.

  HOST-TYPED ARGUMENTS ARE READ STRICTLY. Keys such as domain, host or
  server_name are also used for free text (a topic domain, a podcast host, a
  display name), so for those keys the WHOLE value must be ASCII hostname
  shaped -- [a-z0-9.-] labels, the separator, more labels, an optional
  ':port' -- and must run to the closing quote. CJK prose in such a field
  (醫療。AI 應用, 王小明。Guest: Amy, 東京サーバー。Tokyo-1) is therefore not read.

  SCOPE AND LIMITS, stated honestly. (1) Not covered: case variation
  (EVIL.COM) and a plain trailing root dot (evil.com.) -- they are the same
  bytes as ordinary URLs. (2) Not covered by this rule: fullwidth-letter
  hostnames with only ASCII dots (ｅｖｉｌ.ｃｏｍ) -- ATR-2026-00444 sees those;
  cloud-metadata hosts written with separators also hit ATR-2026-00013. (3) Not
  covered: a bare URL in prose or in a non-URL argument (a chat message, a
  document body, a search query); that form is undecidable from Chinese
  punctuation. A URL passed under a key outside the lists above (q, query,
  text, content, input) is a known gap. (4) Not
  covered: punycode (xn--) spellings of a blocked IDN, percent-encoded host
  bytes, and a trailing separator that ends the value. (5) A security test
  suite or advisory that reproduces the serialized call verbatim will match.

  RE2 PORTABILITY. Both conditions are written for RE2-family engines (Go
  regexp, Rust regex) as well as JavaScript and Python re: the five separator
  characters and the fullwidth letter/digit ranges are written as literal
  characters rather than \\uXXXX escapes (which RE2 spells \\x{XXXX} and JS
  without the u flag does not), there is no lookahead or lookbehind, and
  every repeat bound is at most 253. The "not the last character of the
  value" exclusion is expressed by requiring a following label character,
  delimiter or ':port' after the separator instead of a negative lookahead,
  so the matched behaviour is unchanged.
author: "ATR Community (CVE sync)"
date: "2026/10/22"
schema_version: "0.1"
detection_tier: pattern
maturity: test
severity: medium

references:
  cve:
    - "CVE-2026-107288"
  cwe:
    - "CWE-918"
    - "CWE-1289"
    - "CWE-176"
  owasp_llm:
    - "LLM02:2025"
    - "LLM06:2025"
  owasp_agentic:
    - "ASI02:2026"
  mitre_atlas:
    - "AML.T0053 - AI Agent Tool Invocation"
  mitre_attack:
    - "T1090 - Proxy"
  external:
    - "https://nvd.nist.gov/vuln/detail/CVE-2026-107288"
    - "https://github.com/pydantic/pydantic-ai/commit/a9dab92099d0ef9d5d4aa34ccac8a6f1b0e51284"
    - "https://github.com/pydantic/pydantic-ai/commit/c1f212a084cbfa0012f2044cdb4731d214b3b983"
    - "https://github.com/pydantic/pydantic-ai/commit/490335f8e2322e143a79337ddca9410e0176c812"
    - "https://github.com/pydantic/pydantic-ai/releases/tag/v1.107.6"
    - "https://www.unicode.org/reports/tr46/"

metadata_provenance:
  cve: human-reviewed
  cwe: human-reviewed
  owasp_llm: human-reviewed
  owasp_agentic: human-reviewed
  mitre_atlas: human-reviewed
  mitre_attack: human-reviewed

compliance:
  eu_ai_act:
    - article: "15"
      context: "Article 15 (accuracy, robustness and cybersecurity) calls for resilience against attempts to circumvent security controls. This rule provides detection evidence supporting that requirement by flagging a fetch-tool URL whose host is spelled with an IDNA label separator so that a string-compared domain block list is bypassed."
      strength: primary
    - article: "10"
      context: "Article 10 (data and data governance) concerns which data an AI system draws on. An SSRF fetch of a blocked internal host pulls unauthorised data into the agent's context; this rule provides detection evidence supporting control over that data path."
      strength: secondary
  nist_ai_rmf:
    - subcategory: "MS.2.7"
      context: "MS.2.7 requires security and resilience of the AI system to be evaluated. Counting tool calls whose URL host carries a non-ASCII label separator measures whether the fetch tool's domain control actually holds against normalisation-based bypass."
      strength: primary
    - subcategory: "MS.2.10"
      context: "MS.2.10 covers privacy risk. A blocked internal or metadata host reached through SSRF can expose credentials and personal data to the model; this rule surfaces the attempt for that assessment."
      strength: secondary
  iso_42001:
    - clause: "8.1"
      context: "ISO/IEC 42001 Clause 8.1 (operational planning and control): the fetch tool's domain block list is an operational control, and this rule reports arguments crafted to slip past it before IDNA normalisation."
      strength: primary
    - clause: "6.2"
      context: "ISO/IEC 42001 Clause 6.2 (AI objectives and planning): keeping agent egress inside approved destinations is a security objective, and this rule supplies runtime evidence of attempts to defeat it."
      strength: secondary

tags:
  category: context-exfiltration
  subcategory: ssrf-idna-label-separator-host
  scan_target: runtime
  confidence: high
  source: cve-disclosure

agent_source:
  type: tool_call
  framework:
    - any
  provider:
    - any

detection:
  condition: any
  conditions:
    - field: tool_args
      operator: regex
      value: '\\?["\x27](?:[a-z]{0,16}_?ur[il]|href|link|src|endpoint|location|website|site|page|target)\\?["\x27]\s{0,3}[:=]\s{0,3}\\?["\x27]\s{0,3}(?:[a-z][a-z0-9+.-]{0,15}:)?//[^\s/?#"\x27\\。．｡․﹒]{0,253}(?:[。．｡․﹒]|\\u(?:3002|ff0e|ff61|2024|fe52))(?:[a-z0-9-]|[０-９Ａ-Ｚａ-ｚ]|[/?#]|:\d)'
      description: "A quoted URL-typed argument whose HOST component (between '//' and the first '/', '?' or '#') contains an IDNA label separator (U+3002, U+FF0E, U+FF61) or look-alike dot (U+2024, U+FE52), literal or JSON-escaped, followed by another label, a delimiter or a port -- the CVE-2026-107288 blocked_domains bypass shape."
    - field: tool_args
      operator: regex
      value: '\\?["\x27](?:host|hostname|domain|[a-z]{1,12}_host|server_name)\\?["\x27]\s{0,3}[:=]\s{0,3}\\?["\x27]\s{0,3}[a-z0-9.-]{1,253}(?:[。．｡․﹒]|\\u(?:3002|ff0e|ff61|2024|fe52))[a-z0-9-](?:[a-z0-9.-]|[。．｡․﹒]|\\u(?:3002|ff0e|ff61|2024|fe52)){0,253}(?::\d{1,5})?\\?["\x27]'
      description: "The same separator inside a bare host-typed argument (host / hostname / domain / *_host / server_name) that a tool resolves directly -- the scheme-less form of the same normalisation bypass. The whole value must be an ASCII hostname (labels, separators, optional :port) running to the closing quote, so CJK free text in such a field is not read."
  false_positives:
    - "Security test suites, CVE reproductions and advisories that quote the serialized tool call verbatim (for example the upstream tests/test_ssrf.py fixtures) match -- same bytes as the attack."
    - "A URL argument whose host was copied out of East Asian text together with a full stop AND has more host text after it (https://example.com。cn/...) matches. That value does not resolve as written by a strict parser and does resolve to a different host after IDNA folding, so it is reported deliberately."
    - "A link / href / url field populated from scraped prose can carry a sentence-final full stop followed by an ASCII word, for example {\"link\":\"https://t.co。Thanks\"}. That value matches, because it is byte-for-byte the same shape as https://evil。com and cannot be told apart by pattern."
    - "Not matched by design: a separator in the PATH, QUERY or FRAGMENT (https://zh.wikipedia.org/wiki/句號。, ?q=台北。天氣), a separator that is the last character of the value, punycode xn-- hosts, native IDN hosts such as bücher.example, and any URL that appears in prose or a non-URL argument."

response:
  actions:
    - alert
  message_template: >
    [ATR-2026-02866] A fetch-tool URL or host argument spells its hostname with a
    non-ASCII label separator (U+3002 / U+FF0E / U+FF61 / U+2024 / U+FE52). DNS
    resolution folds these to '.', so a string-compared domain block list can be
    bypassed (CVE-2026-107288). Normalise the host with IDNA/UTS #46 before any
    allow/block-list check and re-evaluate this call.

confidence: 78

test_cases:
  true_positives:
    - input: "{\"tool_name\":\"web_fetch\",\"arguments\":{\"url\":\"https://evil。com/page\"}}"
      expected: triggered
      description: "CVE-2026-107288 evidence (upstream test_blocked_domains_folds_idna): U+3002 between two labels of a blocked host"
    - input: "{\"tool_name\":\"web_fetch\",\"arguments\":{\"url\":\"https://evil.com．/page\"}}"
      expected: triggered
      description: "CVE-2026-107288 evidence: U+FF0E used as a trailing root separator before the path"
    - input: "{\"tool_name\":\"web_fetch\",\"arguments\":{\"url\":\"https://evil.com｡/page\"}}"
      expected: triggered
      description: "CVE-2026-107288 evidence: U+FF61 halfwidth ideographic full stop"
    - input: "{\"tool_name\":\"web_fetch\",\"arguments\":{\"url\":\"https://evil.com․/page\"}}"
      expected: triggered
      description: "CVE-2026-107288 evidence: U+2024 one dot leader"
    - input: "{\"tool_name\":\"web_fetch\",\"arguments\":{\"url\":\"https://internal-admin。corp。example/api/keys\"}}"
      expected: triggered
      description: "CVE-2026-107288 evidence: an internal admin host spelled entirely with U+3002"
    - input: "{\"tool_name\":\"web_fetch\",\"arguments\":{\"url\":\"https://evil\\u3002com/page\"}}"
      expected: triggered
      description: "Derived variant: the same call logged by a Python hook with json.dumps(ensure_ascii=True), so the separator is the escape \\u3002"
    - input: "{\"tool_name\":\"http_get\",\"arguments\":{\"target_url\":\"http://intranet﹒corp:8443/admin\"}}"
      expected: triggered
      description: "Derived variant: U+FE52 small full stop, a different URL key and an explicit port"
    - input: "{\"tool_name\":\"dns_lookup\",\"arguments\":{\"hostname\":\"internal-admin．corp．example\"}}"
      expected: triggered
      description: "Derived variant: scheme-less host argument with U+FF0E separators"
    - input: "{\"tool_name\":\"connect_db\",\"arguments\":{\"db_host\":\"pg-primary。internal:5432\"}}"
      expected: triggered
      description: "Derived variant: *_host key with U+3002 separator and an explicit port"
    - input: "{\"tool_name\":\"dns_lookup\",\"arguments\":{\"hostname\":\"internal-admin\\u3002corp\\u3002example\"}}"
      expected: triggered
      description: "Derived variant: host-typed argument logged by a Python hook with ensure_ascii=True (escaped \\u3002)"
    - input: "{\"tool_name\":\"crawl\",\"arguments\":{\"website\":\"https://evil。com/\"}}"
      expected: triggered
      description: "Derived variant: website key (reviewer-reported miss in round 1)"
    - input: "{\"tool_name\":\"web_fetch\",\"arguments\":{\"url\":\"https://evil。ｃｏｍ/page\"}}"
      expected: triggered
      description: "Derived variant: U+3002 followed by a fullwidth-letter label (exercises the literal fullwidth range kept in the RE2 rewrite)"
    - input: "{\"tool_name\":\"dns_lookup\",\"arguments\":{\"host\":\"metadata﹒internal\"}}"
      expected: triggered
      description: "Derived variant: U+FE52 small full stop in a scheme-less host argument (literal character in the RE2 rewrite)"
  true_negatives:
    - input: "{\"tool_name\":\"web_fetch\",\"arguments\":{\"url\":\"https://example.com/page\"}}"
      expected: not_triggered
      description: "BENIGN TWIN: ordinary web_fetch call on the same tool and argument"
    - input: "{\"tool_name\":\"web_fetch\",\"arguments\":{\"url\":\"https://xn--bcher-kva.example/page\"}}"
      expected: not_triggered
      description: "BENIGN TWIN: a punycode IDN host, the legitimate ASCII-compatible form"
    - input: "{\"tool_name\":\"web_fetch\",\"arguments\":{\"url\":\"https://bücher.example/page\"}}"
      expected: not_triggered
      description: "BENIGN TWIN: a native Unicode IDN host with ordinary ASCII dots"
    - input: "{\"tool_name\":\"web_fetch\",\"arguments\":{\"url\":\"https://zh.wikipedia.org/wiki/句號。Wiki\"}}"
      expected: not_triggered
      description: "BENIGN TWIN: U+3002 in the PATH followed by ASCII -- outside the host component"
    - input: "{\"tool_name\":\"web_fetch\",\"arguments\":{\"url\":\"https://www.google.com/search?q=台北。weather\"}}"
      expected: not_triggered
      description: "BENIGN TWIN: U+3002 in the query string"
    - input: "{\"tool_name\":\"web_fetch\",\"arguments\":{\"url\":\"https://example.com。\"}}"
      expected: not_triggered
      description: "BENIGN TWIN: a URL extracted from a Chinese sentence with its trailing full stop -- the separator ends the value"
    - input: "{\"tool_name\":\"send_message\",\"arguments\":{\"text\":\"請參考 https://example.com。謝謝\"}}"
      expected: not_triggered
      description: "BENIGN TWIN: Chinese sentence-final full stop right after a URL, followed by CJK text"
    - input: "{\"tool_name\":\"send_message\",\"arguments\":{\"text\":\"網址是 https://github.com。GitHub 上也有 CI/CD 說明\"}}"
      expected: not_triggered
      description: "BENIGN TWIN: full stop followed by an ASCII word in prose -- not a URL-typed argument, so not read"
    - input: "{\"tool_name\":\"dns_lookup\",\"arguments\":{\"hostname\":\"api.example.com\"}}"
      expected: not_triggered
      description: "Ordinary host-typed argument"
    - input: "請參考 https://example.com。謝謝"
      expected: not_triggered
      description: "Raw Chinese prose with a URL and a sentence-final full stop"
    - input: "{\"tool_name\":\"web_fetch\",\"arguments\":{\"url\":\"https://example.com/\\u8def\\u5f91\\u3002\"}}"
      expected: not_triggered
      description: "Python-escaped Chinese path ending in an escaped U+3002 -- outside the host"
    - input: "{\"tool_name\":\"classify\",\"arguments\":{\"domain\":\"醫療。AI 應用\"}}"
      expected: not_triggered
      description: "BENIGN TWIN: domain key holding a CJK topic phrase with a full stop followed by ASCII (round-1 FP)"
    - input: "{\"tool_name\":\"podcast_note\",\"arguments\":{\"host\":\"王小明。Guest: Amy\"}}"
      expected: not_triggered
      description: "BENIGN TWIN: host key meaning a podcast host, CJK name then an ASCII word (round-1 FP)"
    - input: "{\"tool_name\":\"create_vm\",\"arguments\":{\"server_name\":\"東京サーバー。Tokyo-1\"}}"
      expected: not_triggered
      description: "BENIGN TWIN: server_name display label in Japanese followed by an ASCII tag (round-1 FP)"
    - input: "{\"tool_name\":\"connect\",\"arguments\":{\"db_host\":\"本番DB。Primary\"}}"
      expected: not_triggered
      description: "BENIGN TWIN: *_host key holding a Japanese label, not a hostname (round-1 FP)"
    - input: "{\"tool_name\":\"set_config\",\"arguments\":{\"domain\":\"example.com。\"}}"
      expected: not_triggered
      description: "BENIGN TWIN: host-typed value whose separator is the last character (copied sentence stop)"
    - input: "{\"tool_name\":\"crawl\",\"arguments\":{\"website\":\"https://example.com/about\"}}"
      expected: not_triggered
      description: "BENIGN TWIN: ordinary website argument with ASCII dots"