Sn Infographic

sn-infographic

Info graphic generation scene skill (tier 1), relying on the sn-image-generate, sn-image-recognize, and sn-text-optimize tools provided by sn-image-base (tier 0).

Features:

• Evaluation of prompt quality (auto mode)
• Prompt expansion (force/auto mode)
• Multiple rounds of image generation and VLM review
• Output the best result based on quality ranking

Input Specification

Who extracts what: Main Agent parameter extraction resolves max_rounds, output_mode, prompts_expand_mode, and aspect_ratio / image_size (each only when the user gives an explicit value). aspect_ratio and image_size without an explicit value are inferred by the Worker in Step 0.

API Configuration

All API calls in this skill are executed through the sn_agent_runner.py of the sn-image-base skill, with authentication parameters using default values (CLI > environment variables > built-in defaults),无需显式传入。

When encountering MissingApiKeyError or needing to specify a model: pass explicitly via CLI parameters, parameter reference $SN_IMAGE_BASE/references/api_spec.md.

$SN_IMAGE_BASE path explanation: $SN_IMAGE_BASE is the installation directory of the sn-image-base skill (SKILL.md exists). The agent can locate this path by skill name sn-image-base in the list of installed skills.

Architecture: Main Agent + Worker Agent

This skill uses a two-tier agent architecture:

Responsibility Boundaries:

• Worker Agent does not send any messages to the user directly, only returns structured JSON
• Main Agent is responsible for sending all user-visible messages
• Worker Agent's last message must be and only be the JSON string defined in the Return Contract
• Worker Agent's internal VLM calls always execute directly, without spawning subagents

Workflow

Main Agent Workflow

1. Parameter extraction from the user request, in three passes:

   1. Inline KV directives — parse tokens of the form key=value where key ∈ {max_rounds, output_mode, prompts_expand_mode, aspect_ratio, image_size}; strip recognized tokens from the user message, and the remainder becomes user_prompt. Example: "生成一张信息图 max_rounds=3 output_mode=verbose" → user_prompt="生成一张信息图", max_rounds=3, output_mode=verbose.

   2. Keyword recognition (case-insensitive, applied to the stripped text) — fill any parameter not yet set by inline KV using the table below:

      Parameter	Trigger keywords	Resolved value
      output_mode	verbose, 详细, 详尽, 完整统计	verbose
      	friendly, 简洁, 精简	friendly
      max_rounds	N 轮, N rounds, 重试 N 次 (parse N)	N, clamped to [1, 8]
      prompts_expand_mode	强制扩写, force expand, force expansion	force
      	不扩写, 跳过扩写, disable expansion, no expand	disable
      aspect_ratio	an explicit supported ratio (16:9 9:16 4:3 3:4 1:1 2:3 3:2 4:5 5:4 21:9 9:21), with or without a 宽高比 / 画面比例 / 比例 / aspect ratio lead-in	that ratio (validated against the supported set in runtime-parameters.md; unsupported value → leave unset for Worker inference)
      image_size	an explicit supported size (2k 4k), with or without an image_size / 分辨率 / 清晰度 / image size lead-in	that size (vague quality words like 高清 / 超清 do not count); unsupported value → leave unset for Worker inference

   3. Defaults — any parameter still unset falls back to max_rounds=1, output_mode=friendly, prompts_expand_mode=auto. aspect_ratio and image_size have no Main-Agent default: when no explicit value is detected they are left unset for the Worker to infer in Step 0.

   Precedence: inline KV > keyword recognition > default. Values from inline KV are validated against the Input Specification (out-of-range max_rounds clamped to [1, 8]; unrecognized enum values fall back to default and Main Agent should log the mismatch).

2. Send uniform preflight message: "Using sn-infographic skill to generate infographic, please wait..."

3. Start Worker Agent (Sub-Agent), passing in complete parameters and working directory

4. When Worker Agent returns status=ok and need_main_agent_send=true:

   • max_rounds = 1: Generate the Text Summary (see Output Format → friendly mode for length/language rules) from expanded_prompt in the returned JSON (always present for status=ok, see Return Contract), send it, then send the rank=1 single image
   • max_rounds > 1, friendly mode: Generate the Text Summary based on the rank=1 round's result and violations, send it, then send the rank=1 single image
   • max_rounds > 1, verbose mode: Render the verbose template (see Output Format → verbose mode for substitution rules) and send it, then send all images in rank order

5. If Worker Agent returns status=error, report the real error field content to the user

Worker Agent Workflow

Worker Agent receives user_prompt, max_rounds, prompts_expand_mode, an optional aspect_ratio and image_size (each set only when the user gave an explicit value), and the working directory of this skill (SKILL_DIR). (output_mode stays on the Main Agent side — Worker has no branch that depends on it.)

Worker Environment

Variables referenced as $NAME in the bash snippets below. Worker must bind each before the step that consumes it.

Naming: $SKILL_DIR for own files; $SN_<SKILL_NAME> (e.g. $SN_IMAGE_BASE) for cross-skill references.

JSON parsing: every sn_agent_runner.py ... -o json call prints a JSON envelope on stdout ({"status", "result", "model", ...}; diagnostics go to stderr). A failed call sets status to a non-ok value (e.g. failed) and omits result, so always confirm .status == ok on the envelope before reading .result — otherwise a missing .result surfaces as the literal null, which is itself valid JSON and slips past both jq -r and extract_json.py (no error raised). The LLM's own JSON (evaluation / analysis steps) lives inside the result string and may carry stray prose or ```json fences. Before any jq, pipe the runner output through $SN_IMAGE_BASE/scripts/extract_json.py (reads stdin, prints the recovered JSON, exits non-zero when none is found); for steps that parse the inner LLM/VLM JSON, pipe .result through it as well. A non-ok status or a non-zero extract_json.py exit means the response is unusable → return the Error Flow JSON.

Step 0 — Initialization

1. Generate task_id (timestamp, format YYYYMMDD_HHMMSS) and create the uniform temporary directory /tmp/openclaw/sn-infographic/<task_id>/ as TEMP_DIR. TEMP_DIR must exist before any subsequent step writes to it:

   TASK_ID=$(date +%Y%m%d_%H%M%S)
   TEMP_DIR="/tmp/openclaw/sn-infographic/${TASK_ID}"
   mkdir -p "$TEMP_DIR"
   

2. Initialize an empty rounds list

3. Resolve aspect_ratio and image_size (bind to ASPECT_RATIO / IMAGE_SIZE): use the explicit Main Agent value when present, else infer from user_prompt per $SKILL_DIR/references/runtime-parameters.md. Defaults: aspect_ratio → 16:9; image_size inference currently has a single option, 2k.

Step 1 — Decide whether to rewrite the image prompt (always runs)

This step decides whether to rewrite/expand the user's image-generation prompt text before Step 3 generates the image, and produces the boolean should_expand. When Step 2 is skipped it also sets EXPANDED_PROMPT and records prompts_expand_skipped = true.

Scope (do not over-read the step name). "Expand" here means rewriting the text prompt for image generation, nothing more. This is not task decomposition, plan generation, or a plan-review gate, and Step 1 starts no agents of its own — it is a single sn-text-optimize call made by the Worker itself. Do not map it onto any subagent-driven-development / delegate_task-style workflow, and write no plan files. (The Worker is the only sub-agent this skill uses, started once by the Main Agent; the Worker spawns none of its own — see Responsibility Boundaries.)

PROMPTS_EXPAND_MODE is the already-resolved input handed over by the Main Agent — Step 1 acts on it, it does not re-parse the user request. Resolving the mode value (Main Agent parameter extraction) and running this decision are two different jobs: completing the former does not complete Step 1. Do not skip this step; in auto mode the evaluation call below is mandatory — never infer should_expand from the prompt's apparent quality.

Only Step 2 (prompt expansion) is ever skipped, and only when this step decides so. The branch depends on PROMPTS_EXPAND_MODE:

auto mode (default):

1. Run the evaluation call (mandatory). The inner evaluation JSON lives inside .result; its schema is $SKILL_DIR/references/evaluation-standard.md (required_results, optional_results).

   EVAL_ENVELOPE=$(python "$SN_IMAGE_BASE/scripts/sn_agent_runner.py" sn-text-optimize \
     --system-prompt-path "$SKILL_DIR/references/evaluation-standard.md" \
     --user-prompt "$USER_PROMPT" \
     --output-format json | python "$SN_IMAGE_BASE/scripts/extract_json.py")
   
   # A failed runner envelope (status != ok) carries no .result.
   EVAL_STATUS=$(printf '%s' "$EVAL_ENVELOPE" | jq -r '.status')
   
   EVAL=$(printf '%s' "$EVAL_ENVELOPE" | jq -r '.result' \
     | python "$SN_IMAGE_BASE/scripts/extract_json.py")
   

2. Decide should_expand:

   • required_pass: all answer in required_results are "yes"
   • optional_pass: count of answer="yes" in optional_results / total ≥ 0.6
   • should_expand = not (required_pass and optional_pass)

3. Conservative fallback: if EVAL_STATUS is not ok (the evaluation call itself failed) or extract_json.py exits non-zero, default should_expand = true. Unlike Steps 2.0 / 2.3, a failed evaluation does not abort the Worker — auto falls back to expanding.

4. If should_expand = true: execute Step 2.

5. If should_expand = false: skip Step 2, set EXPANDED_PROMPT to the original prompt, record prompts_expand_skipped = true:

   EXPANDED_PROMPT="$USER_PROMPT"
   echo "$EXPANDED_PROMPT" > "$TEMP_DIR/expanded-prompt.txt"
   

force mode:

• Skip the evaluation, always execute Step 2 (expansion is mandatory).
• prompts_expand_skipped is not recorded — the field appears in the Return JSON only when Step 2 is skipped (see Return Contract rules).

disable mode:

• Skip both the evaluation and Step 2; use user_prompt directly as expanded_prompt:

  EXPANDED_PROMPT="$USER_PROMPT"
  echo "$EXPANDED_PROMPT" > "$TEMP_DIR/expanded-prompt.txt"
  

• Record prompts_expand_skipped = true.

Step 2 — Content Analysis + Layout & Style Selection + Prompt Expansion

2.0 Content Analysis (using sn-image-base's sn-text-optimize tool):

ANALYSIS_ENVELOPE=$(python "$SN_IMAGE_BASE/scripts/sn_agent_runner.py" sn-text-optimize \
  --system-prompt-path "$SKILL_DIR/references/analysis-framework.md" \
  --user-prompt "$USER_PROMPT" \
  --output-format json | python "$SN_IMAGE_BASE/scripts/extract_json.py")

Save the inner analysis JSON from .result (not the envelope, so Step 2.1 can jq data_type / tone / audience directly) to $TEMP_DIR/analysis.json. The guard below rejects a failed envelope first (status not ok or extract_json.py non-zero → Error Flow with .error):

# A failed runner envelope (status != ok) has no .result → return Error Flow.
if [ "$(printf '%s' "$ANALYSIS_ENVELOPE" | jq -r '.status')" != "ok" ]; then
  ANALYSIS_ERROR=$(printf '%s' "$ANALYSIS_ENVELOPE" | jq -r '.error')
  # return Error Flow JSON {"status":"error","error":"$ANALYSIS_ERROR"} to Main Agent and stop
fi

printf '%s' "$ANALYSIS_ENVELOPE" | jq -r '.result' \
  | python "$SN_IMAGE_BASE/scripts/extract_json.py" > "$TEMP_DIR/analysis.json"

Schema: $SKILL_DIR/references/analysis-framework.md (defines data_type, tone, audience, and the other fields consumed by Step 2.1 / 2.2).

2.1 Layout & Style Selection

This is a name-level, weighted-random pick from the candidate tables in $SKILL_DIR/references/layout-style-selection.md; it operates purely on layout/style names. Do NOT open any file under references/layouts/ or references/styles/ here, and do not "compare options" to choose a best fit — the pick is random, not reasoned over file contents. The one selected layout file and one selected style file are read exactly once, later, in Step 2.3.

1. Read analysis result from temporary directory $TEMP_DIR/analysis.json;

ANALYSIS=$(cat "$TEMP_DIR/analysis.json")

2. From data_type / tone / audience, run the candidate lookup + weighted-random sampling defined in $SKILL_DIR/references/layout-style-selection.md to obtain one LAYOUT name and one STYLE name (names only — no file reads);
3. Validate the selection by checking the definition files exist (existence only via [ -f ], still no reading); fall back to hub-spoke + corporate-memphis if missing:

[ -f "$SKILL_DIR/references/layouts/${LAYOUT}.md" ] || LAYOUT=hub-spoke
[ -f "$SKILL_DIR/references/styles/${STYLE}.md" ] || STYLE=corporate-memphis

4. Save selection result to temporary directory: $TEMP_DIR/layout-style.json;

Format of layout-style.json:

{
  "layout": "<layout>",
  "style": "<style>"
}

2.2 Structured Content Generation

Read analysis result and structured content template, convert user_prompt into a design-ready structured content based on the template rules:

ANALYSIS=$(cat "$TEMP_DIR/analysis.json")
LAYOUT_STYLE=$(cat "$TEMP_DIR/layout-style.json")
STRUCTURED_CONTENT_TEMPLATE=$(cat "$SKILL_DIR/references/structured-content-template.md")

Follow the three phases defined in the template (High-Level Outline → Section Development → Data Integrity Check), combine the learning objectives, visual opportunities, and key data in analysis.json, generate structured content, and save it to the temporary directory:

cat > "$TEMP_DIR/structured-content.md" << 'EOF'
<Content generated based on structured-content-template.md format>
EOF

Structure: $SKILL_DIR/references/structured-content-template.md.

Rules: All data must be preserved exactly. Do not rewrite. Do not add information that is not in the source.

2.3 Prompt Expansion (using sn-image-base's sn-text-optimize tool):

Read layout/style selection, then assemble the system prompt by direct file concatenation (do not use heredocs — layout/style files contain backticks and $(...) that an unquoted heredoc body would execute):

LAYOUT=$(jq -r '.layout' "$TEMP_DIR/layout-style.json")
STYLE=$(jq -r '.style' "$TEMP_DIR/layout-style.json")

{
  cat "$SKILL_DIR/references/prompts-expand-system.md"
  printf '\n\n---\n\n## Selected Layout: %s\n\n' "$LAYOUT"
  cat "$SKILL_DIR/references/layouts/${LAYOUT}.md"
  printf '\n\n---\n\n## Selected Style: %s\n\n' "$STYLE"
  cat "$SKILL_DIR/references/styles/${STYLE}.md"
  printf '\n\n---\n\n## Output Template Reference\n\n'
  cat "$SKILL_DIR/references/base-prompt.md"
} > "$TEMP_DIR/expand-system-prompt.md"

Use the content of structured-content.md as user-prompt (passed via --user-prompt-path to avoid argv-length and quoting issues), read system prompt from temporary file and call sn-text-optimize:

EXPAND_ENVELOPE=$(python "$SN_IMAGE_BASE/scripts/sn_agent_runner.py" sn-text-optimize \
  --system-prompt-path "$TEMP_DIR/expand-system-prompt.md" \
  --user-prompt-path "$TEMP_DIR/structured-content.md" \
  --output-format json | python "$SN_IMAGE_BASE/scripts/extract_json.py")

Extract the result field as expanded_prompt and write to temporary directory. Here .result is the expanded prompt text (not JSON), so only the envelope is parsed via extract_json.py. Confirm .status == ok first: a failed envelope has no .result, so jq -r '.result' would yield the literal string null and write "null" as the image prompt:

# A failed runner envelope (status != ok) has no .result → return Error Flow.
if [ "$(printf '%s' "$EXPAND_ENVELOPE" | jq -r '.status')" != "ok" ]; then
  EXPAND_ERROR=$(printf '%s' "$EXPAND_ENVELOPE" | jq -r '.error')
  # return Error Flow JSON {"status":"error","error":"$EXPAND_ERROR"} to Main Agent and stop
fi

EXPANDED_PROMPT=$(printf '%s' "$EXPAND_ENVELOPE" | jq -r '.result')
echo "$EXPANDED_PROMPT" > "$TEMP_DIR/expanded-prompt.txt"

expanded-prompt.txt: single UTF-8 string, passed verbatim to sn-image-generate --prompt in Step 3.

Beyond the status guard above, if parsing fails or truncation is suspected (the returned content is incomplete), the Worker must likewise return the Error Flow JSON (status=error, real message) and terminate — it must not message the user directly (see Responsibility Boundaries).

Step 3 — Image Generation Loop

Execute round ROUND from 1 to max_rounds sequentially. Inside each iteration set the shell variable ROUND to the current round number, and use ${ROUND} in every path so successive rounds do not overwrite each other:

for ROUND in $(seq 1 "$MAX_ROUNDS"); do
  # the Generate Image / Review Image / Save Round Result blocks below run inside this loop body
  :
done

Generate Image (using sn-image-base's sn-image-generate tool):

python "$SN_IMAGE_BASE/scripts/sn_agent_runner.py" sn-image-generate \
  --prompt "$EXPANDED_PROMPT" \
  --image-size "$IMAGE_SIZE" \
  --aspect-ratio "$ASPECT_RATIO" \
  --save-path "$TEMP_DIR/round_${ROUND}.png" \
  -o json

Review Image (only executed when max_rounds > 1):

• If no VLM model is configured: return Error Flow JSON suggesting the user add a VLM configuration or set max_rounds=1.
• If the VLM call fails/times out: no fallback; return Error Flow JSON with the real error.

python "$SN_IMAGE_BASE/scripts/sn_agent_runner.py" sn-image-recognize \
  --system-prompt-path "$SKILL_DIR/references/prompts-critic-system.md" \
  --user-prompt "Evaluate the diagram in the image against the rules. Output your assessment." \
  --images "$TEMP_DIR/round_${ROUND}.png" \
  --output-format json

Map VLM response into the per-round record (the VLM response schema is defined in $SKILL_DIR/references/prompts-critic-system.md; each violation is a four-field object):

• vlm.result → rounds[i].result (verbatim — "PASS" or "FAIL")
• vlm.violations → rounds[i].violations (passthrough verbatim — array of { rule_id, rule_name, detail, revised_description } objects)
• len(vlm.violations) → rounds[i].violations_count
• vlm.reasoning → rounds[i].reasoning (verbatim string passthrough)

When max_rounds=1 (no VLM call), default the round record to result="PASS", violations=[], violations_count=0, reasoning="".

Save Round Result：

{
  "round": 1,
  "image": "$TEMP_DIR/round_1.png",
  "result": "PASS|FAIL",
  "violations_count": 1,
  "violations": [
    {
      "rule_id": "5",
      "rule_name": "Illegible Text",
      "detail": "<offending element description>",
      "revised_description": "<suggested fix per the prompts-critic-system.md standards>"
    }
  ],
  "reasoning": "<VLM reasoning, or \"\" when max_rounds=1>",
  "timing": {
    "image_generation": { "elapsed_seconds": 12.34, "model": "sn_image_model" },
    "vlm_review": { "elapsed_seconds": 5.67, "model": "sensenova-6.8-flash-lite" }
  }
}

Early Termination Check (only executed when max_rounds > 1):

• If result=PASS, immediately exit the loop, do not continue generating
• If result=FAIL, continue to the next round (if there are remaining rounds)

Step 4 — Image Quality Ranking

Sort images by violations_count ascending + round ascending, return structured JSON to Main Agent.

Return Contract

After Worker Agent completes, its last message must be and only be the following JSON string (bare JSON, no code fences, no preceding or trailing text).

Notation in the examples below:

• <...> — documentation placeholder; replace with the real value at runtime.
• A|B — one of the listed literals; the returned JSON must contain exactly one of them (e.g. "result": "PASS" or "result": "FAIL", never the literal string "PASS|FAIL").
• $VAR — must be expanded to the resolved value before serialization. For example, "image": "$TEMP_DIR/round_1.png" in the schema must be returned as the absolute path actually written by Step 3 (e.g. "/tmp/openclaw/sn-infographic/20260521_120000/round_1.png"), never the literal "$TEMP_DIR/round_1.png".
• Conditional fields — every field whose Rules entry says "omitted when …" must be physically absent from the JSON in that case, not present-with-null.

Normal Flow:

{
  "status": "ok",
  "need_main_agent_send": true,
  "expanded_prompt": "<original user_prompt if prompts_expand_skipped, else expanded result from Step 2.3>",
  "prompts_expand_skipped": true,
  "early_terminated": true,
  "timing": {
    "total_elapsed_seconds": 35.12,
    "prompt_evaluation": { "elapsed_seconds": 2.11, "model": "sensenova-6.8-flash-lite" },
    "content_analysis": { "elapsed_seconds": 3.22, "model": "sensenova-6.8-flash-lite" },
    "prompt_expand": { "elapsed_seconds": 8.45, "model": "sensenova-6.8-flash-lite" }
  },
  "rounds": [
    {
      "round": 1,
      "image": "$TEMP_DIR/round_1.png",
      "result": "PASS|FAIL",
      "violations_count": 1,
      "violations": [
        {
          "rule_id": "5",
          "rule_name": "Illegible Text",
          "detail": "<offending element description>",
          "revised_description": "<suggested fix>"
        }
      ],
      "reasoning": "<VLM reasoning, or \"\" when max_rounds=1>",
      "timing": {
        "image_generation": { "elapsed_seconds": 12.34, "model": "sn_image_model" },
        "vlm_review": { "elapsed_seconds": 5.67, "model": "sensenova-6.8-flash-lite" }
      }
    }
  ]
}

Error Flow:

{
  "status": "error",
  "error": "<Actual error information>"
}

Rules:

• status=ok must contain need_main_agent_send: true.
• expanded_prompt: always present in status=ok; value is original user_prompt when prompts_expand_skipped=true, else the Step 2.3 result.
• prompts_expand_skipped: present (true) only when Step 2 is skipped (prompts_expand_mode=disable, or auto with passing evaluation); omitted otherwise.
• early_terminated: present (true) only when Step 3 exited the loop early via a PASS; omitted otherwise (including all max_rounds=1 runs).
• violations: array of objects from the VLM response, schema $SKILL_DIR/references/prompts-critic-system.md (rule_id, rule_name, detail, revised_description). [] when result=PASS or max_rounds=1.
• violations_count: len(violations); 0 when max_rounds=1.
• reasoning: VLM reasoning field verbatim; "" when max_rounds=1.
• When max_rounds=1, the single round's result defaults to "PASS" (image delivered without VLM check).
• Top-level timing:
  • total_elapsed_seconds: Worker wall time from Step 0 to JSON return.
  • prompt_evaluation: {elapsed_seconds, model} from Step 1 evaluation. Present only when prompts_expand_mode=auto.
  • content_analysis: {elapsed_seconds, model} from Step 2.0. Omitted when prompts_expand_skipped=true.
  • prompt_expand: {elapsed_seconds, model} from Step 2.3. Omitted when prompts_expand_skipped=true.
• rounds[].timing.image_generation.model: hardcoded "sn_image_model" (sn-image-generate returns no model field).
• rounds[].timing.vlm_review: omitted when max_rounds=1.

Output Format

friendly mode (default)

Text Summary — a one-sentence description generated by Main Agent. Length: ≤ 50 chars/字 regardless of language (1 Chinese character = 1 unit, 1 ASCII character = 1 unit). Language: follow the dominant language of user_prompt (predominantly Chinese → output Chinese; otherwise → output English).

• when max_rounds = 1: derive the description from expanded_prompt (focus on what the infographic depicts).
• when max_rounds > 1: derive the description from the rank=1 round's result and violations:
  • result=PASS: positive tone.
  • result=FAIL (1–2 violations): briefly point out the specific issues.
  • result=FAIL (≥ 3 violations): objectively summarize the main issues.

Image: rank=1 single image.

verbose mode

Quality ranking result (high -> low)
---
Expanded prompt: [expanded | not expanded, using original prompt]
<expanded_prompt>
---
#1 round=<n> result=<PASS|FAIL> violations=<n> [early terminated]
#2 round=<n> result=<PASS|FAIL> violations=<n>
...
---
Time statistics: Total <total>s | Prompt evaluation <t>s | Content analysis <t>s | Prompt expansion <t>s | Image generation <t>s×<n> rounds | VLM review <t>s×<n> rounds
---
Images (sent in rank order)

Substitution rules:

Call Relationship

• Bottom-level dependency: sn-image-base → sn-image-generate, sn-image-recognize, sn-text-optimize

References

• references/analysis-framework.md - Analysis methodology
• references/base-prompt.md - Prompt template
• references/evaluation-standard.md - Evaluation standard
• references/layout-style-selection.md - Layout and style selection rules
• references/prompts-expand-system.md - Prompt expansion system prompt
• references/prompts-critic-system.md - Prompt critic system prompt
• references/runtime-parameters.md - Runtime parameters
• references/structured-content-template.md - Structured content template
• references/layouts/<layout>.md - Layout definitions (87 layouts)
• references/styles/<style>.md - Style definitions (66 styles)

Read only the selected layout/style file (in Step 2.3); never bulk-read these two directories to choose — selection is name-level and random (Step 2.1).