framework: port R4 credential-helper pair from brain 15f6979a (python entrypoint w/ alpine bash-path candidates + impl, byte-faithful; P0-SEC T125)
(cherry picked from commit 13e7398c2a)
This commit is contained in:
code-be-01
@@ -1,220 +1,64 @@
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#!/bin/bash
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# git-credential-mosaic — git credential helper. Resolves a Gitea token from the
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# Mosaic credential store at runtime so remote URLs never embed secrets.
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#!/usr/bin/python3
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# git-credential-mosaic — production entrypoint (P0-SEC R4, rev-code-02 B1).
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#
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# Install (one-time, per clone or globally):
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# git config credential.helper "$HOME/.config/mosaic/tools/git/git-credential-mosaic"
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# WHY THIS IS NOT BASH: three review rounds falsified every in-bash startup
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# guard. A non-interactive bash sources $BASH_ENV and imports exported
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# functions BEFORE the first script line, so read(), unset(), exit(),
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# declare(), printf() — every callable — can be shadows that fake the
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# ancestry, defeat the scrub, or forge diagnostics (rev-code-02 probes 1 and
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# 2, artifacts fc49e9d9 lineage). No in-language dispatch survives that.
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#
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# Per-agent identity (Gate-16 author != reviewer separation):
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# git config mosaic.gitIdentity <agent-id> # per-worktree, persists on disk
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# # or: export MOSAIC_GIT_IDENTITY=<agent-id>
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# This entrypoint is unshapable at the bash level: python does not read
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# BASH_ENV and imports no bash functions, and the interpreter is pinned by
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# absolute shebang (no PATH resolution). It builds the child environment BY
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# ALLOWLIST and execve's the bash implementation directly — the child bash
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# starts with no BASH_ENV, no BASH_FUNC_*, no SHELLOPTS/BASHOPTS, and exactly
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# the variables the credential protocol needs. stdin/stdout/stderr and argv
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# pass through untouched.
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#
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# ── WHY THIS FAILS CLOSED ──────────────────────────────────────────────────────
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# This helper used to end by emitting the shared account's token for any request
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# it could not resolve to an identity. A seat with no identity, or with an
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# identity whose token was never provisioned, therefore received the most
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# privileged credential configured on the host — silently, and indistinguishably
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# from correct operation. Every record it then created (commit, push, PR, review)
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# was attributed to that shared account, so author != reviewer separation was
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# unenforceable and the true actor was unrecoverable after the fact.
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#
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# Under-provisioning must fail loudly, not impersonate. A refused git operation
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# is recoverable in one command; a merged pull request attributed to the wrong
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# principal is not.
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#
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# ── CONTRACT ───────────────────────────────────────────────────────────────────
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# identity : MOSAIC_GIT_IDENTITY > git config mosaic.gitIdentity > the
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# username git supplies on stdin
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# store : chosen by what the identity IS, with no precedence and no
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# cross-store fallback (see "Credential store selection" below)
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# hit : emit username + password, exit 0
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# miss : emit NOTHING, spool a durable escalation record, explain on
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# stderr, exit 1 — git surfaces the failure and nothing is attributed
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# unknown host : exit 0 with no output, no record (passthrough for non-Mosaic
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# remotes handled by another helper)
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#
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# Backward compatibility is preserved for exactly one case: a host with no fleet
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# and no identity requested still gets the shared account, because on such a host
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# the shared account is the operator's own and there is no attribution to lose.
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# A host that HAS a fleet has agents whose records must be distinguishable, so
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# the shared fallback is refused there.
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#
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# A token is never written to stderr, to the escalation record, or to any log.
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# The implementation file (git-credential-mosaic.impl) refuses to run without
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# the clean-mode marker, so it cannot be invoked directly as a shaped-entry
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# bypass of this wrapper.
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[ "$1" = "get" ] || exit 0
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import os
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import sys
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host=""; username_in=""
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while IFS= read -r line; do
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[ -z "$line" ] && break
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case "$line" in
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host=*) host=${line#host=};;
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username=*) username_in=${line#username=};;
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esac
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done
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IMPL = os.path.join(os.path.dirname(os.path.realpath(__file__)), "git-credential-mosaic.impl")
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# Absolute-path candidates ONLY — never PATH resolution (an attacker-shaped
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# PATH must not choose the interpreter). /usr/bin/bash is the fleet-host
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# layout; /bin/bash is alpine and other FHS variants (found by the T125
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# gateway-image verification: the hardcoded /usr/bin/bash made every call
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# exit 127 inside node:22-alpine).
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BASH_CANDIDATES = ("/usr/bin/bash", "/bin/bash")
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BASH = next((p for p in BASH_CANDIDATES if os.access(p, os.X_OK)), None)
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# Recognized Gitea hosts carry the per-identity token scheme. Anything else is
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# declined quietly — another helper owns it, and refusing would break it.
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case "$host" in
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git.uscllc.com) idpfx=gitea-usc;;
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git.mosaicstack.dev) idpfx=gitea-mosaicstack;;
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*) exit 0;;
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esac
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# Allowlist: everything else in the environment dies at this boundary. Adding
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# a variable here is a security decision — it crosses into a shell that no
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# longer has any startup shaping, but it also becomes the only context the
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# implementation can see.
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KEEP = (
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"HOME",
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"PATH",
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"LANG",
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"MOSAIC_GIT_IDENTITY",
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"MOSAIC_AGENT_NAME",
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"MOSAIC_BRAIN_HOME",
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"MOSAIC_CREDENTIAL_SPOOL",
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"MOSAIC_CREDENTIAL_LINEAGE_FENCE",
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)
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ident="$MOSAIC_GIT_IDENTITY"; ident_src="MOSAIC_GIT_IDENTITY"
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if [ -z "$ident" ]; then
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ident=$(git config --get mosaic.gitIdentity 2>/dev/null)
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ident_src="git config mosaic.gitIdentity"
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fi
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if [ -z "$ident" ]; then
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ident="$username_in"
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ident_src="the username git supplied"
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fi
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env = {"_MOSAIC_HELPER_CLEAN": "1"}
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for name in KEEP:
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value = os.environ.get(name)
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if value is not None:
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env[name] = value
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# ── Credential store selection ────────────────────────────────────────────────
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# An identity is a SEAT or it is a SERVICE, and which one it is determines where
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# its credential lives. There is no precedence rule between the two stores and no
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# fallback from one to the other: a seat whose slot is empty fails closed rather
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# than reading a service credential that happens to share its name.
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#
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# seat — <brain>/fleet/agents/<ident>/ exists
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# credential at <brain>/fleet/agents/<ident>/secrets/<idpfx>-<ident>.token
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# service — it does not
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# credential at ~/.config/mosaic/secrets/gitea-tokens/<idpfx>-<ident>.token
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#
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# One credential, one location. Two copies of one credential diverge, and the
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# stale copy fails in a way that reads as a revoked token rather than as drift.
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#
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# Brain-home resolution mirrors packages/mosaic/src/fleet/brain-home.ts and
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# tools/fleet/start-agent-session.sh: MOSAIC_BRAIN_HOME wins, else ~/.mosaic.
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brain_home="${MOSAIC_BRAIN_HOME:-$HOME/.mosaic}"
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svc_store="$HOME/.config/mosaic/secrets/gitea-tokens"
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idtok=""; ident_kind=""
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if [ -n "$ident" ]; then
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if [ -d "$brain_home/fleet/agents/$ident" ]; then
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ident_kind="seat"
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idtok="$brain_home/fleet/agents/$ident/secrets/${idpfx}-${ident}.token"
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else
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ident_kind="service identity"
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idtok="$svc_store/${idpfx}-${ident}.token"
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fi
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if [ -r "$idtok" ]; then
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echo "username=${ident}"
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echo "password=$(cat "$idtok")"
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exit 0
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fi
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fi
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# ── Shared-account fallback: ONLY on a host with no fleet and no identity ──────
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# `fleet/agents` existing is the same signal brain-home.ts uses to decide a brain
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# is active. Where there are seats, records must be attributable, so an
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# unresolvable request is refused instead of borrowing the shared account.
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fleet_present=0
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[ -d "$brain_home/fleet/agents" ] && fleet_present=1
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if [ -z "$ident" ] && [ "$fleet_present" -eq 0 ]; then
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script_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
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# shellcheck source=../_lib/credentials.sh
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source "$script_dir/../_lib/credentials.sh"
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load_credentials "$idpfx" >/dev/null 2>&1 || exit 0
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# GITEA_USER is not populated by load_credentials (it exports GITEA_URL and
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# GITEA_TOKEN only). Gitea's git-over-HTTP auth authenticates from the token in
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# the password field, not from the username string, so any non-empty
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# placeholder works — deliberately NOT a real account name, since framework
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# files stay operator-agnostic (tools/quality/scripts/verify-sanitized.sh).
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echo "username=${GITEA_USER:-git}"
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echo "password=$GITEA_TOKEN"
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exit 0
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fi
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# ── FAIL CLOSED ───────────────────────────────────────────────────────────────
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if [ -z "$ident" ]; then
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reason="no-identity"
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else
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reason="no-token-for-identity"
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fi
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seat="${MOSAIC_AGENT_NAME:-unknown}"
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ts=$(date -u +%Y-%m-%dT%H:%M:%SZ)
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# The escalation RECORD is durable and unconditional; any notification built on
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# top of it is best-effort. Record and alert are deduplicated separately — a cap
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# on the alert alone lets the spool grow without bound exactly while the operator
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# is being told nothing, so the louder the failure the quieter it gets.
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#
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# A record field is arbitrary operator-supplied text: an identity comes from git
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# config or the environment, and cwd is whatever directory git ran in. Either can
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# contain a quote or a backslash, which would make the line unparseable JSON --
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# and a spool that silently stops parsing is worse than no spool, because the
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# operator only discovers it while reading the record that explains an outage.
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json_escape() {
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local s=$1
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s=${s//\\/\\\\}
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s=${s//\"/\\\"}
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s=${s//$'\t'/\\t}
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s=${s//$'\r'/\\r}
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s=${s//$'\n'/\\n}
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printf '%s' "$s"
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}
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spool="${MOSAIC_CREDENTIAL_SPOOL:-$HOME/.local/state/mosaic-credential-escalations}"
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spool_record=""
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if mkdir -p "$spool" 2>/dev/null; then
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chmod 700 "$spool" 2>/dev/null
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spoolfile="$spool/$(date -u +%Y%m%d).jsonl"
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dedupe="$spool/.spooled-${seat}-${ident:-none}-${reason}-$(date -u +%Y%m%d%H%M)"
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if [ ! -e "$dedupe" ]; then
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: > "$dedupe" 2>/dev/null
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printf '{"ts":"%s","reason":"%s","identity":"%s","identity_source":"%s","kind":"%s","seat":"%s","host":"%s","cwd":"%s"}\n' \
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"$(json_escape "$ts")" "$(json_escape "$reason")" \
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"$(json_escape "${ident:-<unset>}")" "$(json_escape "$ident_src")" \
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"$(json_escape "${ident_kind:-none}")" "$(json_escape "$seat")" \
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"$(json_escape "$host")" "$(json_escape "$PWD")" \
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>> "$spoolfile" 2>/dev/null
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chmod 600 "$spoolfile" 2>/dev/null
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fi
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# Name the record only if one is actually on disk. Printing the path
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# unconditionally sends the operator to a file that does not exist on exactly
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# the hosts where the spool could not be created.
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[ -s "$spoolfile" ] && spool_record="$spoolfile"
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find "$spool" -maxdepth 1 -name '.spooled-*' -mmin +120 -delete 2>/dev/null
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fi
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cat >&2 <<EOF
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git-credential-mosaic: REFUSED (fail-closed).
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host : ${host}
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identity : ${ident:-<unset>}${ident:+ (from ${ident_src}; resolved as a ${ident_kind})}
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reason : ${reason}
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EOF
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if [ -n "$ident" ]; then
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cat >&2 <<EOF
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expected : ${idtok}
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EOF
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fi
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cat >&2 <<EOF
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No per-identity credential resolved. This helper does NOT fall back to the shared
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account: that fallback makes every record it creates attributable to one
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principal, which is unrecoverable once a pull request has merged under it.
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Fix (pick one):
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export MOSAIC_GIT_IDENTITY=<agent-id> # process-scoped
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git config mosaic.gitIdentity <agent-id> # per-repo/worktree, persists
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Then provision that identity's credential at the path named above. An identity
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with a directory under \${MOSAIC_BRAIN_HOME:-\$HOME/.mosaic}/fleet/agents/ is a
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seat and is read ONLY from its own secrets/ slot; any other identity is read from
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~/.config/mosaic/secrets/gitea-tokens/. There is no fallback between the two.
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If this identity legitimately needs git access and has none, ask the orchestrator
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to provision one.
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EOF
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if [ -n "$spool_record" ]; then
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echo " record: ${spool_record}" >&2
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else
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echo " record: NOT WRITTEN — spool unavailable at ${spool}" >&2
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fi
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exit 1
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argv = [BASH, IMPL] + sys.argv[1:]
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if BASH is None:
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sys.stderr.write("git-credential-mosaic: no executable bash at " + " or ".join(BASH_CANDIDATES) + "\n")
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sys.exit(127)
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try:
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os.execve(BASH, argv, env)
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except OSError as exc:
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sys.stderr.write(f"git-credential-mosaic: entrypoint exec failed: {exc}\n")
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sys.exit(127)
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